Merge pull request #278 from tnmyk/main

Added Merge Sort

Author: hhhrrrttt222111

ALGORITHMS/Sorting/MergeSort/MergeSort.cpp

@@ -0,0 +1,69 @@
+#include<iostream>
+using namespace std;
+
+void swapping(int &a, int &b) {     
+   int temp;
+   temp = a;
+   a = b;
+   b = temp;
+}
+void display(int *array, int size) {
+   for(int i = 0; i<size; i++)
+      cout << array[i] << " ";
+   cout << endl;
+}
+void merge(int *array, int l, int m, int r) {
+   int i, j, k, nl, nr;
+   //size of left and right sub-arrays
+   nl = m-l+1; nr = r-m;
+   int larr[nl], rarr[nr];
+   //fill left and right sub-arrays
+   for(i = 0; i<nl; i++)
+      larr[i] = array[l+i];
+   for(j = 0; j<nr; j++)
+      rarr[j] = array[m+1+j];
+   i = 0; j = 0; k = l;
+   //marge temp arrays to real array
+   while(i < nl && j<nr) {
+      if(larr[i] <= rarr[j]) {
+         array[k] = larr[i];
+         i++;
+      }else{
+         array[k] = rarr[j];
+         j++;
+      }
+      k++;
+   }
+   while(i<nl) {       //extra element in left array
+      array[k] = larr[i];
+      i++; k++;
+   }
+   while(j<nr) {     //extra element in right array
+      array[k] = rarr[j];
+      j++; k++;
+   }
+}
+void mergeSort(int *array, int l, int r) {
+   int m;
+   if(l < r) {
+      int m = l+(r-l)/2;
+      // Sort first array
+      mergeSort(array, l, m);
+      // Sort second array
+      mergeSort(array, m+1, r);
+
+      // merge both
+      merge(array, l, m, r);
+   }
+}
+int main() {
+   int n;
+   cin >> n;    // Number of elements in array
+   int arr[n];     
+   for(int i = 0; i<n; i++) {
+      cin >> arr[i];        // Inputting elements into array.
+   }
+   mergeSort(arr, 0, n-1);     // r = n-1 for last index
+   cout << "Sorted Array";
+   display(arr, n);
+}

ALGORITHMS/Sorting/MergeSort/readme.md

@@ -0,0 +1,6 @@
+# Merge Sort
+Mergesort is a divide and conquer algorithm that was invented by John von Neumann in 1945.
+
+It recursively divides the input array into two halves, calls itself for the two halves, and then merges the two sorted halves.
+
+Time Complexity is O(nlogn).