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Copy pathMergeSort.java
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60 lines (51 loc) · 1.7 KB
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package Recursion;
import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) {
int[] arr = {5, 4, 3, 2, 1};
arr = mergeSort(arr);
// int[] ans = mergeSort(arr);
System.out.println(Arrays.toString(arr));
}
static int[] mergeSort(int[] arr){
if (arr.length == 1){
// base condition.
return arr;
}
int mid = arr.length/2;
int[] left = mergeSort(Arrays.copyOfRange(arr, 0, mid)) ;
int[] right= mergeSort(Arrays.copyOfRange(arr, mid, arr.length));
return merge(left, right);
}
private static int[] merge(int[] first, int[] second){
int[] mix = new int[first.length + second.length];
// Taking a pointer for these three arrays (first, second & mix)
int i = 0; // index pointer for 1st array
int j = 0; // index pointer for 2nd (divided) arrays
int k = 0; // index pointer for a new array in which first and second are going to merge.
while(i< first.length && j< second.length){
if (first[i] < second[j]){
mix[k] = first[i];
i++;
}else{
mix[k] = second[j];
j++;
}
k++;
}
// it may be possible that one of the array is not complete
// copy the remaining elements.
while (i< first.length){
mix[k] = first[i];
i++;
k++;
}
while (j< second.length){
mix[k] = second[j];
j++;
k++;
}
return mix;
}
}
// Original array is not modified indeed it returns the copy of array which is sorted.