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3.MergeSort.cpp

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+/*
+ * This program takes an array from the user
+ * sorts it using merge sort
+ * Prints the sorted array
+ * Time Complexity of the algorithm is: O(nlogn)
+ *
+ * For more information about Merge Sort Algorithm: https://en.wikipedia.org/wiki/Merge_sort
+ *
+ *      Coded by: Abdurrezak EFE
+ *
+ * */
+#include <iostream>
+#include <algorithm>
+using namespace std;
+
+void merge(int arr[], int l, int m, int r) //merge function O(n)
+{
+    int lsize = m-l+1;
+    int rsize = r-m;
+
+    int left[lsize];
+    int right[rsize];
+
+    for(int i=0;i<lsize;i++)
+        left[i] = arr[i+l];
+
+    for(int i=0;i<rsize;i++)
+        right[i] = arr[i+m+1];
+
+    int li=0,ri=0;
+    int index = l;
+
+    while(li<lsize && ri<rsize)
+    {
+        if(left[li] <= right[ri])
+            arr[index]=left[li],li++;
+        else
+            arr[index] = right[ri],ri++;
+
+        index++;
+    }
+
+    while(li<lsize)
+        arr[index] = left[li],li++,index++;
+
+    while(ri<rsize)
+        arr[index] = right[ri],ri++,index++;
+
+}
+
+void merge_sort(int arr[],int l, int r) //merge sort function O(nlogn)
+{
+    if(l<r)
+    {
+        int m = (l+r)/2;
+        merge_sort(arr,l,m);
+        merge_sort(arr,m+1,r);
+        merge(arr,l,m,r);
+    }
+}
+
+int main()
+{
+    int k;
+    cout << "Enter the number of the integers you want to construct the array from: ";
+    cin >> k;
+
+    int arr[k];
+    for(int i=0;i<k;i++)
+        cin >> arr[i];
+
+    merge_sort(arr,0,k-1); //sorting
+
+    for(int i=0;i<k;i++) //printing the array
+        cout << arr[i] << " ";
+}