归并排序的思想

#include <iostream>
#include <vector>
using namespace std;
void mergeSort(vector<int>& nums, int l, int r) {
    if (l >= r) {
        return;
    }
    int mid = (l + r) / 2;
    mergeSort(nums, l, mid);
    mergeSort(nums, mid + 1, r);
    vector<int> temp(r - l + 1);
    int i = l, j = mid + 1, k = 0;
    while (i <= mid && j <= r) {
        if (nums[i] < nums[j]) {
            temp[k++] = nums[i++];
        } else {
            temp[k++] = nums[j++];
        }
    }
    while (i <= mid) {
        temp[k++] = nums[i++];
    }
    while (j <= r) {
        temp[k++] = nums[j++];
    }
    for (int i = l; i <= r; ++i) {
        nums[i] = temp[i - l];
    }
}
int main() {
    vector<int> nums {5, 1, 9, 3, 7, 4, 8, 6, 2};
    mergeSort(nums, 0, nums.size() - 1);
    for (auto num : nums) {
        cout << num << " ";
    }
    return 0;
}