C Merge Sort - rFronteddu/general_wiki GitHub Wiki

#include <iostream>
#include <vector>

// Merges two subarrays of array[].
// First subarray is arr[left..mid]
// Second subarray is arr[mid+1..right]
void merge(std::vector<int>& arr, int left, int mid, int right) {
    int n1 = mid - left + 1;
    int n2 = right - mid;

    // Create temporary vectors
    std::vector<int> l(n1), r(n2);

    // Copy data to temp vectors
    for (int i = 0; i < n1; i++) l[i] = arr[left + i];
    for (int j = 0; j < n2; j++) r[j] = arr[mid + 1 + j];

    // Merge the temp vectors back into arr[left..right]
    int i = 0, j = 0, k = left;
    while (i < n1 && j < n2) {
        if (l[i] <= r[j]) arr[k++] = l[i++];
        else arr[k++] = r[j++];
    }

    // Copy the remaining elements if any
    while (i < n1) arr[k++] = l[i++];
    while (j < n2) arr[k++] = r[j++];
}

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

    // Sort first and second halves
    mergeSort(arr, left, mid);
    mergeSort(arr, mid + 1, right);

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

int main() {
    std::vector<int> data = {12, 11, 13, 5, 6, 7};

    mergeSort(data, 0, data.size() - 1);

    std::cout << "Sorted array: ";
    for (int num : data) std::cout << num << " ";
    return 0;
}