leetcode 1738. 找出第 K 大的异或坐标值

题目传送门

链接：https://leetcode-cn.com/problems/find-kth-largest-xor-coordinate-value/

题干

题解

二重循环枚举，sum[i][j]表示子矩阵 [i, j] 的异或和

sum[i][j] = matrix[i][j] ^ sum[i - 1][j] ^ sum[i][j - 1] ^ sum[i - 1][j - 1]

最后再排序查找第k大的数字即可

Code

class Solution {
public:
    int kthLargestValue(vector<vector<int>>& matrix, int k) {
        int arr[1000005], m = matrix.size(), n = matrix[0].size();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (i > 0)
                    matrix[i][j] ^= matrix[i - 1][j];
                if (j > 0)
                    matrix[i][j] ^= matrix[i][j - 1];
                if (i * j > 0)
                    matrix[i][j] ^= matrix[i - 1][j - 1]; 
                arr[i * n + j] = matrix[i][j];
            }
        }
        sort(arr, arr + m * n);
        return arr[m*n - k];
    }
};