C++归并排序的递归与非递归实现

递归实现C++代码如下：

#include <iostream>#include <vector>void merge(std::vector<int>& arr, int left, int mid, int right) {    int n1 = mid - left + 1;    int n2 = right - mid;    std::vector<int> L(n1);    std::vector<int> R(n2);    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];    }    int i = 0;    int j = 0;    int k = left;    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(std::vector<int>& arr, int left, int right) {    if (left < right) {        int mid = left + (right - left) / 2;        mergeSort(arr, left, mid);        mergeSort(arr, mid + 1, right);        merge(arr, left, mid, right);    }}int main() {    std::vector<int> arr = {12, 11, 13, 5, 6, 7};    int n = arr.size();    mergeSort(arr, 0, n - 1);    std::cout << "Sorted array: ";    for (int i = 0; i < n; i++) {        std::cout << arr[i] << " ";    }    std::cout << std::endl;    return 0;}

非递归实现C++代码如下：

#include <iostream>#include <vector>void merge(std::vector<int>& arr, int left, int mid, int right) {    int n1 = mid - left + 1;    int n2 = right - mid;    std::vector<int> L(n1);    std::vector<int> R(n2);    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];    }    int i = 0;    int j = 0;    int k = left;    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(std::vector<int>& arr) {    int n = arr.size();    int curr_size;    int left_start;    for (curr_size = 1; curr_size <= n - 1; curr_size = 2 * curr_size) {        for (left_start = 0; left_start < n - 1; left_start += 2 * curr_size) {            int mid = std::min(left_start + curr_size - 1, n - 1);            int right = std::min(left_start + 2 * curr_size - 1, n - 1);            merge(arr, left_start, mid, right);        }    }}int main() {    std::vector<int> arr = {12, 11, 13, 5, 6, 7};        mergeSort(arr);    std::cout << "Sorted array: ";    for (int i = 0; i < arr.size(); i++) {        std::cout << arr[i] << " ";    }    std::cout << std::endl;    return 0;}

这两种方法都是通过将数组分成两半，递归或迭代地对每一半进行排序，然后再将两个有序的子数组合并成一个有序的数组。