题解 | #排序#

归并排序

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 将给定数组排序
     * @param arr int整型vector 待排序的数组
     * @return int整型vector
     */
    vector<int> MySort(vector<int>& arr) {
        // write code here
        mergesort(arr, arr.size());
        return arr;
    }
    void mergesort(vector<int>& arr, int n)
    {
        vector<int> temparr(n, 0);
        msort(arr, temparr, 0, n - 1);
    }
    
    void msort(vector<int>& arr, vector<int>& temparr, int left, int right)
    {
        if(left < right)
        {
            int mid = (left + right) / 2;
            msort(arr, temparr, left, mid);
            msort(arr, temparr, mid + 1, right);
            merge(arr, temparr, left, mid, right);
        }
    }
    void merge(vector<int>& arr, vector<int>& temparr, int left, int mid, int right)
    {
        int lposition = left;
        int rposition = mid + 1;

        int k = left;
        
        while(lposition <= mid && rposition <= right)
        {
            if(arr[lposition] < arr[rposition])
            {
                temparr[k++] = arr[lposition++];
            }
            else
            {
                temparr[k++] = arr[rposition++];
            }
        }
        while(lposition <= mid)
        {
            temparr[k++] = arr[lposition++];
        }
        while(rposition <= right)
        {
            temparr[k++] = arr[rposition++];
        }
        while(left <= right)
        {
            arr[left] = temparr[left];
            left++;
        }
    }
};