天池 在线编程 矩阵还原（前缀和）

输入:
2
2
[[1,3],[4,10]]
输出: [[1,2],[3,4]]

Explanation:
before:
1 2
3 4

after:
1 3
4 10

class Solution {
public:
    /**
     * @param n: the row of the matrix
     * @param m: the column of the matrix
     * @param after: the matrix
     * @return: restore the matrix
     */
    vector<vector<int>> matrixRestoration(int n, int m, vector<vector<int>> &after) {
        // write your code here
        for(int i = n-1; i >= 0; --i)
        {
            for(int j = m-1; j >= 0; --j)
            {
                after[i][j] = after[i][j]-(j>0 ? after[i][j-1] : 0)-(i>0 ? after[i-1][j] : 0)
                                +(i>0&&j>0? after[i-1][j-1] : 0);
            }
        }
        return after;
    }
};