Merge pull request #110 from sourishphate/master

MERGE SORT ALGORITHM

Author: GauravWalia19

CodeBase/merge_sort.cpp

@@ -0,0 +1,112 @@
+/**
+ * PROBLEM: Merge Sort in C++
+ * AUTHOR: sourishphate
+ **/
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+/**
+ * This function merges two sorted halves of an array
+ * 
+ * @param A: the array to be sorted
+ * @param low: starting index of the first half
+ * @param mid: ending index of the first half
+ * @param high: ending index of the second half
+ **/
+void merge(vector<int>& A, int low, int mid, int high) {
+    int n1 = mid - low + 1; // Length of first half
+    int n2 = high - mid;    // Length of second half
+
+    vector<int> L(n1); // Create temp arrays
+    vector<int> R(n2);
+
+    // Copy data to temporary arrays L[] and R[]
+    for (int i = 0; i < n1; i++) {
+        L[i] = A[low + i];
+    }
+    for (int j = 0; j < n2; j++) {
+        R[j] = A[mid + 1 + j];
+    }
+
+    int i = 0; // Initial index of first subarray
+    int j = 0; // Initial index of second subarray
+    int k = low; // Initial index of merged subarray
+
+    while (i < n1 && j < n2) {
+        if (L[i] <= R[j]) {
+            A[k] = L[i];
+            i++;
+        } else {
+            A[k] = R[j];
+            j++;
+        }
+        k++;
+    }
+
+    // Copy the remaining elements of L[], if any
+    while (i < n1) {
+        A[k] = L[i];
+        i++;
+        k++;
+    }
+
+    // Copy the remaining elements of R[], if any
+    while (j < n2) {
+        A[k] = R[j];
+        j++;
+        k++;
+    }
+}
+
+/**
+ * This function sorts an array using merge sort algorithm
+ * 
+ * @param A: the array to be sorted
+ * @param p: starting index
+ * @param r: ending index
+ **/
+void mergeSort(vector<int>& A, int p, int r) {
+    if (p < r) {
+        int q = (p + r) / 2; // Find the midpoint
+        mergeSort(A, p, q);      // Sort first half
+        mergeSort(A, q + 1, r);  // Sort second half
+        merge(A, p, q, r);        // Merge the two sorted halves
+    }
+}
+
+/**
+ * This function prints the array
+ * 
+ * @param A: the array to print
+ **/
+void printArray(const vector<int>& A) {
+    for (int val : A) {
+        cout << val << " ";
+    }
+    cout << endl;
+}
+
+int main() {
+    int size;
+    cout << "Enter the size of the array: ";
+    cin >> size;
+
+    vector<int> A(size);
+    cout << "Enter the elements of the array:\n";
+    for (int i = 0; i < size; i++) {
+        cin >> A[i];
+    }
+
+    cout << "Unsorted array: ";
+    printArray(A);
+
+    mergeSort(A, 0, A.size() - 1);
+
+    cout << "Sorted array: ";
+    printArray(A);
+
+    return 0;
+}