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。
