MergeSort.cpp

#include <iostream>
#include <vector>

using namespace std;

void merge(vector<int>& arr, int left, int mid, int right) {
    int n1 = mid - left + 1; // Size of the left subarray
    int n2 = right - mid; // Size of the right subarray

    // Create temporary arrays
    vector<int> leftArr(n1);
    vector<int> rightArr(n2);

    // Copy data to temporary arrays
    for (int i = 0; i < n1; i++) {
        leftArr[i] = arr[left + i];
    }
    for (int j = 0; j < n2; j++) {
        rightArr[j] = arr[mid + 1 + j];
    }

    // Merge the temporary arrays back into arr
    int i = 0; // Index of the left subarray
    int j = 0; // Index of the right subarray
    int k = left; // Index of the merged subarray

    while (i < n1 && j < n2) {
        if (leftArr[i] <= rightArr[j]) {
            arr[k] = leftArr[i];
            i++;
        } else {
            arr[k] = rightArr[j];
            j++;
        }
        k++;
    }

    // Copy the remaining elements of leftArr, if any
    while (i < n1) {
        arr[k] = leftArr[i];
        i++;
        k++;
    }

    // Copy the remaining elements of rightArr, if any
    while (j < n2) {
        arr[k] = rightArr[j];
        j++;
        k++;
    }
}

void mergeSort(vector<int>& arr, int left, int right) {
    if (left < right) {
        int mid = left + (right - left) / 2;

        mergeSort(arr, left, mid); // Sort the left half
        mergeSort(arr, mid + 1, right); // Sort the right half

        merge(arr, left, mid, right); // Merge the sorted halves
    }
}

int main() {
    vector<int> arr = {9, 2, 5, 1, 7, 6, 8, 3, 4};
    int n = arr.size();

    cout << "Original array: ";
    for (int num : arr) {
        cout << num << " ";
    }
    cout << endl;

    mergeSort(arr, 0, n - 1);

    cout << "Sorted array: ";
    for (int num : arr) {
        cout << num << " ";
    }
    cout << endl;

    return 0;
}