Java Program for Merge Sort
Merge Sort is a Divide and Conquer algorithm. It divides input array in two halves, calls itself for the two halves and then merges the two sorted halves. The merge() function is used for merging two halves. The merge(arr, l, m, r) is key process that assumes that arr[l..m] and arr[m+1..r] are sorted and merges the two sorted sub-arrays into one.
Java
/* Java program for Merge Sort */ class MergeSort { // Merges two subarrays of arr[]. // First subarray is arr[l..m] // Second subarray is arr[m+1..r] void merge( int arr[], int l, int m, int r) { // Find sizes of two subarrays to be merged int n1 = m - l + 1 ; int n2 = r - m; /* Create temp arrays */ int L[] = new int [n1]; int R[] = new int [n2]; /*Copy data to temp arrays*/ for ( int i= 0 ; i<n1; ++i) L[i] = arr[l + i]; for ( int j= 0 ; j<n2; ++j) R[j] = arr[m + 1 + j]; /* Merge the temp arrays */ // Initial indexes of first and second subarrays int i = 0 , j = 0 ; // Initial index of merged subarry array int k = l; while (i < n1 && j < n2) { if (L[i] <= R[j]) { arr[k] = L[i]; i++; } else { arr[k] = R[j]; j++; } k++; } /* Copy remaining elements of L[] if any */ while (i < n1) { arr[k] = L[i]; i++; k++; } /* Copy remaining elements of R[] if any */ while (j < n2) { arr[k] = R[j]; j++; k++; } } // Main function that sorts arr[l..r] using // merge() void sort( int arr[], int l, int r) { if (l < r) { // Find the middle point int m = (l+r)/ 2 ; // Sort first and second halves sort(arr, l, m); sort(arr , m+ 1 , r); // Merge the sorted halves merge(arr, l, m, r); } } /* A utility function to print array of size n */ static void printArray( int arr[]) { int n = arr.length; for ( int i= 0 ; i<n; ++i) System.out.print(arr[i] + " " ); System.out.println(); } // Driver method public static void main(String args[]) { int arr[] = { 12 , 11 , 13 , 5 , 6 , 7 }; System.out.println( "Given Array" ); printArray(arr); MergeSort ob = new MergeSort(); ob.sort(arr, 0 , arr.length- 1 ); System.out.println( "\nSorted array" ); printArray(arr); } } /* This code is contributed by Rajat Mishra */ |
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