merge_sort.cpp

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#include <iostream>
#include <vector>

void merge(int *arr, int l, int m, int r) {
    int n1 = m - l + 1;
    int n2 = r - m;
 
    std::vector<int> L(n1), R(n2);
 
    for (int i = 0; i < n1; i++) L[i] = arr[l + i];
    for (int j = 0; j < n2; j++) R[j] = arr[m + 1 + j];
 
    int i = 0, j = 0, k = l;
 
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        } else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }
 
    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }
 
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(int *arr, int l, int r) {
    if (l < r) {
        int m = l + (r - l) / 2;
        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);
        merge(arr, l, m, r);
    }
}

void show(int *arr, int size) {
    for (int i = 0; i < size; i++) std::cout << arr[i] << " ";
    std::cout << "\n";
}

int main() {
    int size;
    std::cout << "Enter the number of elements: ";
    std::cin >> size;
 
    if (size <= 0) {
        std::cout << "Invalid size.\n";
        return 1;
    }
 
    int *arr = new int[size];
    std::cout << "Enter the unsorted elements: ";
    for (int i = 0; i < size; ++i) {
        std::cin >> arr[i];
    }
 
    mergeSort(arr, 0, size - 1);
    std::cout << "Sorted array: ";
    show(arr, size);
    delete[] arr;
    return 0;
}