any help with this mess is appreciated. The task here is to sort an array of integers that differ from zero. I think i made two mistakes which i cant manage to solve.
first: i think i made a mistake at the recursive call. The bounds seem to be set the wrong way while merging
second: i also think the sorting process has several errors too
static void mergeSort(int[] init, int lower, int upper) {
if (lower < upper) {
int mid = (lower + upper) / 2;
mergeSort(init, lower, mid);
mergeSort(init, mid+1, upper);
merge(init, lower, mid, upper);
}
}
static void merge(int[] init, int lower, int mid, int upper) {
int length1 = mid - lower; //length of first subarray
int length2 = upper - mid; //length of second subarray
int[] leftArray = new int[length1+1]; //creating left subArray
int[] rightArray = new int[length2+1]; //creating right subArray
for (int i = 0; i < length1; i++) { //copying positions from left partition to left subArray
leftArray[i] = init[lower + i];
}
for (int i = 0; i < length2; i++) { //copying positions from right partition to right subArray
rightArray[i] = init[mid+i];
}
int i = 0; //sorting
int j = 0;
for (int k = lower; k < upper; k++) {
if (leftArray[i] <= rightArray[j]) {
init[k] = leftArray[i];
i++;
} else {
init[k] = rightArray[j];
j++;
}
}
}
Wasn't this the recommended way to do the merge sort step-by-step using static methods:
public static void mergeSort(int[] init, int arrayLength) {
if (arrayLength < 2) {
return;
}
int mid = arrayLength / 2;
int[] left = new int[mid];
int[] right = new int[arrayLength - mid];
for (int i = 0; i < mid; i++) {
left[i] = init[i];
}
for (int i = mid; i < arrayLength; i++) {
right[i - mid] = init[i];
}
mergeSort(left, mid);
mergeSort(right, arrayLength - mid);
merge(init, left, right, mid, arrayLength - mid);
}
public static void merge(
int[] init, int[] left, int[] right, int leftLength, int rightLength) {
int i = 0, j = 0, k = 0;
while (i < leftLength && j < rightLength) {
if (left[i] <= right[j]) {
init[k++] = left[i++];
}
else {
init[k++] = right[j++];
}
}
while (i < leftLength) {
init[k++] = left[i++];
}
while (j < rightLength) {
init[k++] = right[j++];
}
}
Call "mergeSort" with the 1st parameter being the array to be sorted and the 2nd parameter being it's length.
Cheers!
I'm pretty new to java and I'm having some trouble with this project for my class.
Basically I have to write "A Java program to find the value 45.3 from this list ={-3,10,5,24,45.3,10.5} using the binary search method."
And my code for that is here:
public class BinarySearch
{
public static final int NOT_FOUND = -1;
public static int binarySearch(Integer[] a, int x)
{
int low=0;
int high = a.length - 1;
int mid;
while (low <= high)
{
mid = (low + high) / 2;
if (a[mid].compareTo(x)<0)
low = mid + 1;
else if (a[mid].compareTo(x) > 0)
high = mid - 1;
else
return mid;
}
return NOT_FOUND;
}
public static void main(String[] args)
{
int x = (453/10);
int y = (105/10);
int SIZE = 6;
Integer [] a = {-3, 10, 5, 24, x, y};
System.out.println("45.3 found at " +binarySearch(a, x));
}
}
However I realized that it wasn't sorted so I used a simple BubbleSort that I already had and plugged the numbers in here:
class BubbleSort
{
public static void main(String args[])
{
int x = (453/10);
int y = (105/10);
int a[] = {-3, 10, 5, 24, x, y};
int b = a.length;
int c, d, e;
System.out.print("Original Order : ");
for (c = 0; c < b; c++)
{
System.out.print(" " + a[c]);
}
System.out.println("\n");
System.out.print("Ascending Order : ");
for (d=1; d < b; d++)
{
for (c=0; c < b-d; c++)
{
if (a[c] > a[c+1])
{
int f = a[c];
a[c] = a[c+1];
a[c+1] = f;
}
}
}
for(c = 0; c < b; c++)
{
System.out.print(" " + a[c]);
}
}
}
But at the point I'm at in this class I have no idea how to either make the class files work together in someway or put it all into a single .java or .class file.
Any tips?
Thanks!
public class Search {
public final static int NOT_FOUND = -1;
public static double[] bubbleSort(double[] a) {
int length = a.length;
System.out.print("Original Order : ");
for (int i = 0; i < length; i++) {
System.out.print(" " + a[i]);
}
System.out.println("\n");
System.out.print("Ascending Order : ");
for (int i = 1; i < length; i++) {
for (int j = 0; j < length - j; j++) {
if (a[j] > a[j + 1]) {
double f = a[j];
a[j] = a[j + 1];
a[j + 1] = f;
}
}
}
for (int i = 0; i < length; i++) {
System.out.print(" " + a[i]);
}
System.out.println();
return a;
}
public static int binarySearch(double[] a, double x) {
int low = 0;
int high = a.length - 1;
int mid;
while (low <= high) {
mid = (low + high) / 2;
if (a[mid] - x < 0)
low = mid + 1;
else if (a[mid] - x > 0)
high = mid - 1;
else {
return mid;
}
}
return NOT_FOUND;
}
public static void main(String[] args) {
double[] array = { -3, 10, 5.0, 24, 45.3, 10.5 };
double[] sortedArray = bubbleSort(array);
System.out.println(binarySearch(sortedArray, 45.3));
}
}
Start with just copy & pasting the program to merge. Fortunately there wern't any variable collisions.
public class BubbleSortAndBinarySearch
{
public static final int NOT_FOUND = -1;
public static int binarySearch(Integer[] a, int x)
{
int low=0;
int high = a.length - 1;
int mid;
while (low <= high)
{
mid = (low + high) / 2;
if (a[mid].compareTo(x)<0)
low = mid + 1;
else if (a[mid].compareTo(x) > 0)
high = mid - 1;
else
return mid;
}
return NOT_FOUND;
}
public static void main(String[] args)
{
int x = (453/10);
int y = (105/10);
int SIZE = 6;
Integer [] a = {-3, 10, 5, 24, x, y};
int b = a.length;
int c, d, e;
System.out.print("Original Order : ");
for (c = 0; c < b; c++)
{
System.out.print(" " + a[c]);
}
System.out.println("\n");
System.out.print("Ascending Order : ");
for (d=1; d < b; d++)
{
for (c=0; c < b-d; c++)
{
if (a[c] > a[c+1])
{
int f = a[c];
a[c] = a[c+1];
a[c+1] = f;
}
}
}
for(c = 0; c < b; c++)
{
System.out.print(" " + a[c]);
}
System.out.println(); // inserting this will make the result better to read
System.out.println("45.3 found at " +binarySearch(a, x));
}
}
Then, modify the program to handle non-integer values such as 45.3 and 10.5 correctly. Currently this code only works with integers and the value 45.3 is not used except for in the string.
So I'm writing a program that compares Bubble, Selection, Merge, and Quick Sort. All 4 methods are given a randomized array of 1000 elements and I count to see how many times it takes a method to perform to fully sort the array. My question revolves around the placement of my counts. I know I should look at the Big O complexities for each to get a ballpark estimate of the number but I'm just asking if I put the counts in the right spots.
Bubble Sort:
public static int[] bubbleSort(int[] a)
{
boolean done = false;
int n = a.length;
while(done == false)//runs n times
{
done = true;
for(int i = 0; i < n-1; i++)//runs n times
{
if(a[i] > a[i+1])//Swap
{
bubbleCount++;
int temp = a[i];
a[i] = a[i+1];
a[i+1] = temp;
done = false;
}
}
}
return a;
}
Selection Sort:
public static void selectionSort(int[] a )
{
for (int i = 0; i < a.length - 1; i++)
{
int pos = i;
for (int j = i + 1; j < a.length; j++)
{
// increments selection count
selectionCount++;
// if a[j] is less than a[pos], set pos to j
if (a[j] < a[pos])
{
pos = j;
}
}
// swaps a[i] and a[pos]
int temp = a[i];
a[i] = a[pos];
a[pos] = temp;
}
}
Merge Sort:
public static void mergeSort(int [] a)
{
//put counter for checks inside method
int size = a.length;
if(size < 2)//Halt recursion
{
return;
}
int mid = size/ 2;
int leftSize = mid;
int rightSize = size - mid;
int[] left = new int[leftSize];
int[] right = new int[rightSize];
//populate left
for(int i = 0; i < mid; i++)
{
mergeCount++;
left[i] = a[i];
}
//populate right
for(int i = mid; i < size; i++)
{
mergeCount++;
right[i-mid] = a[i];
}
mergeSort(left);
mergeSort(right);
//merge
merge(left, right, a);
}
public static void merge(int[] left, int[] right, int[] a)
{
int leftSize = left.length;
int rightSize = right.length;
int i = 0;//index for left
int j = 0;//index for right
int k = 0;//index for a
while(i < leftSize && j < rightSize)//compares until the end is reach in either
{
if(left[i] <= right[j])
{
//assigns a[k] to left[i] and increments both i and k
a[k] = left[i];
i++;
k++;
}
else
{
//assigns a[k] to right [j] and increments j and k
a[k] = right[j];
j++;
k++;
}
}
//fills in the rest
while(i<leftSize)
{
a[k] = left[i];
i++;
k++;
}
while(j<rightSize)
{
a[k] = right[j];
j++;
k++;
}
}
Quick Sort
public static void quickSort(int[] a, int left, int right)
{
int index = partition(a, left, right);
if(left < index - 1)
{
//increments quickCount and calls quickSort recursively
quickCount++;
quickSort(a, left, index-1);
}
if(index < right)
{
//increments quickCount and calls quicSort recursively
quickCount++;
quickSort(a, index, right);
}
}
public static int partition(int[] a, int left, int right)
{
int i = left;
int j = right;
int pivot = a[((left+right)/2)];
while(i<=j)
{
while(a[i] < pivot)
{
i++;//correct position so move forward
}
while(a[j] > pivot)
{
j--;//correct position
}
if(i <= j)
{
//swaps and increments i and decrements j
int temp = a[i];
a[i] = a[j];
a[j] = temp;
i++;
j--;
}
}
return i;
}
Your counts should be wherever you do a comparison of two values.
The bubbleCount should be moved up above the if because you want to count every comparison not sure the ones where the if clause is true. The selectionCount seems okay. The mergeCount should be moved to where you compare values.
You need to count comparisons, so I would create a method to compare and count:
static int count;
private static boolean isGreaterThan(int i, int j) {
count++;
return i > j;
}
and always use that method to compare values:
instead of:
while(i<=j)
do:
while(!isGreaterThan(i, j))
etc
So these sorting methods sort numbers in a lesser to greater order, how would I reverse these? I've tried reversing the operations but that doesn't seem to work :/
Still trying to learn Java, thank you for the help
//Selection Sort Method
public static void SelectionSort(int a[], int n) {
int smallest;
for (int i = 0; i < a.length - 1; i++) {
smallest = i;
//see if there is a smaller number further in the array
for (int index = i + 1; index < a.length; index++) {
if (a[index] < a[smallest]) {
swap(a, smallest, index);
}
}
}
}
//Selection Sort swap method to call on
public static void swap(int array2[], int first, int second) {
int hold = array2[first];
array2[first] = array2[second];
array2[second] = hold;
}
//Bubble Sort Method
public static void BubbleSort(int a[], int n) {
int i, j, t = 0;
for (i = 0; i < n; i++) {
for (j = 1; j < (n - i); j++) {
if (a[j - 1] > a[j]) {
t = a[j - 1];
a[j - 1] = a[j];
a[j] = t;
}
}
}
}
//Insertion Sort Method
public static void InsertionSort(int a[], int n) {
int insert;
for (int next = 1; next < a.length; next++) {
insert = a[next];
int moveItem = next;
while (moveItem > 0 && a[moveItem - 1] > insert) {
a[moveItem] = a[moveItem - 1];
moveItem--;
}
a[moveItem] = insert;
}
}
//Quick Sort Method
public static void QuickSort(int a[], int low, int high) {
int partitionLoc;
if (low < high) {
partitionLoc = partition(a, low, high);
QuickSort(a, low, partitionLoc - 1);
QuickSort(a, partitionLoc + 1, high);
}
}
public static int partition(int a2[], int left, int right) {
boolean moveLeft = true;
int separator = a2[left];
while (left < right) {
if (moveLeft == true) {
while ((a2[right] >= separator) && (left < right)) {
right--;
}
a2[left] = a2[right];
moveLeft = false;
} else {
while ((a2[left] <= separator) && (left < right)) {
left++;
}
a2[right] = a2[left];
moveLeft = true;
}
}
a2[left] = separator;
return left;
}
You can leave your method as is and reverse the array:
public static void reverse(int[] a) {
for (int i = 0 ; i < a.length / 2 ; i++) {
int t = a[i];
a[i] = a[a.length - 1 - i];
a[a.length - 1 - i] = t;
}
}
int[] a = // ...
whateverSort(a);
reverse(a);
Just reverse the comparison in each sort:
SelectionSort
a[index] < a[smallest] => a[index] > a[smallest]
BubbleSort
a[j - 1] > a[j] => a[j - 1] < a[j]
InsertionSort
a[moveItem - 1] > insert => a[moveItem - 1] < insert
QuickSort
(a2[right] >= separator) => (a2[right] <= separator)
(a2[left] <= separator) => (a2[left] >= separator)
I am new to Java and have tried to implement mergesort in Java. However, even after running the program several times, instead of the desired sorted output, I am getting the same user given input as the output. I would be thankful if someone could help me understand this unexpected behaviour.
import java.io.*;
import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) throws IOException {
BufferedReader R = new BufferedReader(new InputStreamReader(System.in));
int arraySize = Integer.parseInt(R.readLine());
int[] inputArray = new int[arraySize];
for (int i = 0; i < arraySize; i++) {
inputArray[i] = Integer.parseInt(R.readLine());
}
mergeSort(inputArray);
for (int j = 0; j < inputArray.length; j++) {
System.out.println(inputArray[j]);
}
}
static void mergeSort(int[] A) {
if (A.length > 1) {
int q = A.length / 2;
int[] leftArray = Arrays.copyOfRange(A, 0, q);
int[] rightArray = Arrays.copyOfRange(A, q + 1, A.length);
mergeSort(leftArray);
mergeSort(rightArray);
A = merge(leftArray, rightArray);
}
}
static int[] merge(int[] l, int[] r) {
int totElem = l.length + r.length;
int[] a = new int[totElem];
int i, li, ri;
i = li = ri = 0;
while (i < totElem) {
if ((li < l.length) && (ri < r.length)) {
if (l[li] < r[ri]) {
a[i] = l[li];
i++;
li++;
} else {
a[i] = r[ri];
i++;
ri++;
}
} else {
if (li >= l.length) {
while (ri < r.length) {
a[i] = r[ri];
i++;
ri++;
}
}
if (ri >= r.length) {
while (li < l.length) {
a[i] = l[li];
li++;
i++;
}
}
}
}
return a;
}
}
Here is a corrected version of your code:
import java.io.*;
import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) throws IOException{
BufferedReader R = new BufferedReader(new InputStreamReader(System.in));
int arraySize = Integer.parseInt(R.readLine());
int[] inputArray = new int[arraySize];
for (int i = 0; i < arraySize; i++) {
inputArray[i] = Integer.parseInt(R.readLine());
}
mergeSort(inputArray);
for (int j = 0; j < inputArray.length; j++) {
System.out.println(inputArray[j]);
}
}
static void mergeSort(int[] A) {
if (A.length > 1) {
int q = A.length/2;
//changed range of leftArray from 0-to-q to 0-to-(q-1)
int[] leftArray = Arrays.copyOfRange(A, 0, q-1);
//changed range of rightArray from q-to-A.length to q-to-(A.length-1)
int[] rightArray = Arrays.copyOfRange(A,q,A.length-1);
mergeSort(leftArray);
mergeSort(rightArray);
merge(A,leftArray,rightArray);
}
}
static void merge(int[] a, int[] l, int[] r) {
int totElem = l.length + r.length;
//int[] a = new int[totElem];
int i,li,ri;
i = li = ri = 0;
while ( i < totElem) {
if ((li < l.length) && (ri<r.length)) {
if (l[li] < r[ri]) {
a[i] = l[li];
i++;
li++;
}
else {
a[i] = r[ri];
i++;
ri++;
}
}
else {
if (li >= l.length) {
while (ri < r.length) {
a[i] = r[ri];
i++;
ri++;
}
}
if (ri >= r.length) {
while (li < l.length) {
a[i] = l[li];
li++;
i++;
}
}
}
}
//return a;
}
}
When you rebind A in mergeSort():
A = merge(leftArray,rightArray);
this has no effect in inputArray in main().
You need to return the sorted array from mergeSort() similarly to how you return it from merge().
static int[] mergeSort(int[] A) {
...
return A;
}
and in main():
int[] mergedArray = mergeSort(inputArray);
for (int j = 0; j < mergedArray.length; j++) {
System.out.println(mergedArray[j]);
}
The problem is that java is pass by value and not pass by reference... When you are assigning to array A in the merge method you are changing a copy of the reference to A and not the reference to A itself. Therefore you need to pass A into your merge method and make a structural change to A.
The problem lies here:
A = merge(leftArray,rightArray);
Now your merge array does this:
static int[] merge(int[] l, int[] r) {
int[] a = new int[totElem];
// bunch of code
return a;
}
When you started, A was a reference to inputArray. But then you reassigned it to be whatever came out of merge. Unfortunately, that doesn't touch what inputArray is in the main method. That basically says "Oh look at all the work you did... throw it away!"
You could change that with something like
static int[] mergeSort(int[] A) {
// A = merge... // not this
return merge... // use this
}
Then in your main method, you can do
int[] merged = mergeSort(inputArray);
for(int i : merged) System.out.println(i);
public class MergeSort{
public static void sort(int[] in){
if(in.length <2) return; //do not need to sort
int mid = in.length/2;
int left[] = new int[mid];
int right[] = new int[in.length-mid];
for(int i=0; i<mid; i++){ //copy left
left[i] = in[i];
}
for(int i=0; i<in.length-mid; i++){ //copy right
right[i] = in[mid+i];
}
sort(left);
sort(right);
merge(left, right, in);
}
private static void merge(int[] a, int[] b, int[] all){
int i=0, j=0, k=0;
while(i<a.length && j<b.length){ //merge back
if(a[i] < b[j]){
all[k] = a[i];
i++;
}else{
all[k] = b[j];
j++;
}
k++;
}
while(i<a.length){ //left remaining
all[k++] = a[i++];
}
while(j<b.length){ //right remaining
all[k++] = b[j++];
}
}
public static void main(String[] args){
int[] a = {2,3,6,4,9,22,12,1};
sort(a);
for(int j=0; j<a.length; j++){
System.out.print(a[j] + " ");
}
}
}
public void sort(int[] randomNumbersArrray)
{
copy = randomNumbersArrray.clone();
mergeSort(0 , copy.length - 1);
}
private void mergeSort(int low, int high)
{
if(low < high)
{
int mid = ((low + high) / 2);
mergeSort(low, mid); //left side
mergeSort(mid + 1, high); // right side
merge(low, mid, high); //combine them
}
}
private void merge(int low, int mid, int high)
{
int temp[] = new int[high - low + 1];
int left = low;
int right = mid + 1;
int index = 0;
// compare each item for equality
while(left <= mid && right <= high)
{
if(copy[left] < copy[right])
{
temp[index] = copy[left];
left++;
}else
{
temp[index] = copy[right];
right++;
}
index++;
}
// if there is any remaining loop through them
while(left <= mid || right <= high)
{
if( left <= mid)
{
temp[index] = copy[left];
left++;
index++;
}else if(right <= high)
{
temp[index] = copy[right];
right++;
index++;
}
}
// copy back to array
for(int i = 0; i < temp.length; i++)
{
copy[low + i] = temp[i];
}
}
package Sorting;
public class MergeSort {
private int[] original;
private int len;
public MergeSort(int length){
len = length;
original = new int[len];
original[0]=10;
original[1]=9;
original[2]=8;
original[3]=7;
original[4]=6;
original[5]=5;
original[6]=4;
original[7]=3;
original[8]=2;
original[9]=1;
int[] aux = new int[len];
for(int i=0;i<len;++i){
aux[i]=original[i];
}
Sort(aux,0,len);
}
public void Sort(int[] aux,int start, int end){
int mid = start + (end-start)/2;
if(start < end){
Sort(aux, start, mid-1);
Sort(aux, mid, end);
Merge(aux, start, mid, end);
}
}
public void Merge(int[] aux, int start, int mid, int end){// while array passing be careful of shallow and deep copying
for(int i=start; i<=end; ++i)
auxilary[i] = original[i];
int i = start;
int k = start;
int j = mid+1;
while(i < mid && j <end){
if(aux[i] < aux[j]){
original[k++] = aux[i++];
}
else{
original[k++] = aux[j++];
}
}
if(i == mid){
while(j < end){
original[k++] = aux[j++];
}
}
if(j == end){
while(i < mid){
original[k++] = aux[i++];
}
}
}
public void disp(){
for(int i=0;i<len;++i)
System.out.print(original[i]+" ");
}
public static void main(String[] args) {
MergeSort ms = new MergeSort(10);
ms.disp();
}
}
The above codes are a little confused
Never use variables with names: "k", "j", "m",... this makes the code very confusing
Follows the code in an easier way...
import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) {
Integer[] itens = {2,6,4,9,1,3,8,7,0};
Integer[] tmp = new Integer[itens.length];
int left = 0;
int right = itens.length - 1;
mergeSort(itens, tmp, left, right);
System.out.println(Arrays.toString(itens));
}
private static void mergeSort(Integer[] itens, Integer[] tmpArray, int left, int right) {
if(itens == null || itens.length == 0 || left >= right){
return;
}
int midle = (left + right) / 2;
mergeSort(itens, tmpArray, left, midle);
mergeSort(itens, tmpArray, midle + 1, right);
merge(itens, tmpArray, left, midle + 1, right);
}
private static void merge(Integer[] itens, Integer[] tmpArray, int left, int right, int rightEnd) {
int leftEnd = right - 1;
int tmpIndex = left;
while (left <= leftEnd && right <= rightEnd){
if (itens[left] < itens[right] ){
tmpArray[tmpIndex++] = itens[left++];
} else {
tmpArray[tmpIndex++] = itens[right++];
}
}
while (left <= leftEnd) { // Copy rest of LEFT half
tmpArray[tmpIndex++] = itens[left++];
}
while (right <= rightEnd) { // Copy rest of RIGHT half
tmpArray[tmpIndex++] = itens[right++];
}
while(rightEnd >= 0){ // Copy TEMP back
itens[rightEnd] = tmpArray[rightEnd--];
}
}
}
Might as well add my take on this:
Takes two int arrays and merges them.
Where 'result' is an array of size a.length + b.length
public static void merge( int[] a, int[] b, int[] result )
{
int i = 0, j = 0;
while ( true )
{
if ( i == a.length )
{
if ( j == b.length )
return;
result[ i + j ] = b[ j ];
j++;
}
else if ( j == b.length )
{
result[ i + j ] = a[ i ];
i++;
}
else if ( a[ i ] < b[ j ] )
{
result[ i + j ] = a[ i ];
i++;
}
else
{
result[ i + j ] = b[ j ];
j++;
}
}
}
public class MyMergeSort {
private int[] array;
private int[] tempMergArr;
private int length;
public static void main(String a[]){
int[] inputArr = {45,23,11,89,77,98,4,28,65,43};
MyMergeSort mms = new MyMergeSort();
mms.sort(inputArr);
for(int i:inputArr){
System.out.print(i);
System.out.print(" ");
}
}
public void sort(int inputArr[]) {
this.array = inputArr;
this.length = inputArr.length;
this.tempMergArr = new int[length];
doMergeSort(0, length - 1);
}
private void doMergeSort(int lowerIndex, int higherIndex) {
if (lowerIndex < higherIndex) {
int middle = lowerIndex + (higherIndex - lowerIndex) / 2;
// Below step sorts the left side of the array
doMergeSort(lowerIndex, middle);
// Below step sorts the right side of the array
doMergeSort(middle + 1, higherIndex);
// Now merge both sides
mergeParts(lowerIndex, middle, higherIndex);
}
}
private void mergeParts(int lowerIndex, int middle, int higherIndex) {
for (int i = lowerIndex; i <= higherIndex; i++) {
tempMergArr[i] = array[i];
}
int i = lowerIndex;
int j = middle + 1;
int k = lowerIndex;
while (i <= middle && j <= higherIndex) {
if (tempMergArr[i] <= tempMergArr[j]) {
array[k] = tempMergArr[i];
i++;
} else {
array[k] = tempMergArr[j];
j++;
}
k++;
}
while (i <= middle) {
array[k] = tempMergArr[i];
k++;
i++;
}
}
}
very simple and easy to understand
static void sort(char[] data) {
int length = data.length;
if (length < 2)
return;
int mid = length / 2;
char[] left = new char[mid];
char[] right = new char[length - mid];
for(int i=0;i<mid;i++) {
left[i]=data[i];
}
for(int i=0,j=mid;j<length;i++,j++) {
right[i]=data[j];
}
sort(left);
sort(right);
merge(left, right, data);
}
static void merge(char[] left, char[] right, char[] og) {
int i = 0, j = 0, k = 0;
while(i < left.length && j < right.length) {
if (left[i] < right[j]) {
og[k++] = left[i++];
} else {
og[k++] = right[j++];
}
}
while (i < left.length) {
og[k++] = left[i++];
}
while (j < right.length) {
og[k++] = right[j++];
}
}
I have a parallel version of Merge Sort. I am benefiting from the RecursiveAction and ForkJoinPool. Note that the number of workers can be set as a constant. However, I am setting it as the number of available processors on the machine.
import java.util.Arrays;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
public class ParallelMergeSorter {
private int[] array;
public ParallelMergeSorter(int[] array) {
this.array = array;
}
public int[] sort() {
int numWorkers = Runtime.getRuntime().availableProcessors(); // Get number of available processors
ForkJoinPool pool = new ForkJoinPool(numWorkers);
pool.invoke(new ParallelWorker(0, array.length - 1));
return array;
}
private class ParallelWorker extends RecursiveAction {
private int left, right;
public ParallelWorker(int left, int right) {
this.left = left;
this.right = right;
}
protected void compute() {
if (left < right) {
int mid = (left + right) / 2;
ParallelWorker leftWorker = new ParallelWorker(left, mid);
ParallelWorker rightWorker = new ParallelWorker(mid + 1, right);
invokeAll(leftWorker, rightWorker);
merge(left, mid, right);
}
}
private void merge(int left, int mid, int right) {
int[] leftTempArray = Arrays.copyOfRange(array, left, mid + 1);
int[] rightTempArray = Arrays.copyOfRange(array, mid + 1, right + 1);
int leftTempIndex = 0, rightTempIndex = 0, mergeIndex = left;
while (leftTempIndex < mid - left + 1 || rightTempIndex < right - mid) {
if (leftTempIndex < mid - left + 1 && rightTempIndex < right - mid) {
if (leftTempArray[leftTempIndex] <= rightTempArray[rightTempIndex]) {
array[mergeIndex] = leftTempArray[leftTempIndex];
leftTempIndex++;
} else {
array[mergeIndex] = rightTempArray[rightTempIndex];
rightTempIndex++;
}
} else if (leftTempIndex < mid - left + 1) {
array[mergeIndex] = leftTempArray[leftTempIndex];
leftTempIndex++;
} else if (rightTempIndex < right - mid) {
array[mergeIndex] = rightTempArray[rightTempIndex];
rightTempIndex++;
}
mergeIndex++;
}
}
}
}
public class MergeTwoSortedArray {
public void approach_2(int[] arr1, int[] arr2) {
List<Integer> result = IntStream.concat(Arrays.stream(arr1), Arrays.stream(arr2)).boxed().sorted()
.collect(Collectors.toList());
System.out.println(result);
}
public void approach_3(Integer[] arr1, Integer[] arr2) {
List<Integer> al1 = Arrays.asList(arr1);
List<Integer> al2 = Arrays.asList(arr2);
List<Integer> result = new ArrayList<>();
int i = 0, j = 0;
while (i < al1.size() && j < al2.size()) {
if (al1.get(i) < al2.get(j)) {
result.add(al1.get(i));
i++;
} else {
result.add(al2.get(j));
j++;
}
}
while (i < al1.size()) {
result.add(al1.get(i));
i++;
}
while (j < al2.size()) {
result.add(al2.get(j));
j++;
}
System.out.println(result);
}
public static void main(String[] args) {
MergeTwoSortedArray obj = new MergeTwoSortedArray();
int[] arr1 = { 3, 6, 76, 85, 91 };
int[] arr2 = { 1, 6, 78, 89, 95, 112 };
obj.approach_2(arr1, arr2);
Integer[] arr3 = { 3, 6, 76, 85, 91 };
Integer[] arr4 = { 1, 6, 78, 89, 95, 112 };
obj.approach_3(arr3, arr4);
}
}