leetcode

1074.cpp (800B)

 class Solution {
   public:
     int numSubmatrixSumTarget(vector<vector<int>> &matrix, int target) const {
         const int n = size(matrix), m = size(matrix[0]);
 
         for (int i = 0; i < n; i++) {
             for (int j = 0, acc = 0; j < m; j++) {
                 matrix[i][j] = acc += matrix[i][j];
             }
         }
 
         unordered_map<int, int> um;
         int res = 0;
 
         for (int i = 0; i < m; i++) {
             for (int j = i; j < m; j++) {
                 um = {{0, 1}};
                 int crnt = 0;
                 for (int k = 0; k < n; k++) {
                     crnt += matrix[k][j] - (i > 0 ? matrix[k][i - 1] : 0);
                     res += um[crnt - target];
                     um[crnt]++;
                 }
             }
         }
 
         return res;
     }
 };