- Difficulty: Hard
- Tags: LeetCode, Hard, Array, Hash Table, Matrix, Prefix Sum, leetcode-1074, O(m^2 * n), O(n)
Problem
Given a matrix
and a target
, return the number of non-empty submatrices that sum to target.
A submatrix x1, y1, x2, y2
is the set of all cells matrix[x][y]
with x1 <= x <= x2
and y1 <= y <= y2
.
Two submatrices (x1, y1, x2, y2)
and (x1', y1', x2', y2')
are different if they have some coordinate that is different: for example, if x1 != x1'
.
Example 1:
Input: matrix = [[0,1,0],[1,1,1],[0,1,0]], target = 0 Output: 4 Explanation: The four 1x1 submatrices that only contain 0.
Example 2:
Input: matrix = [[1,-1],[-1,1]], target = 0 Output: 5 Explanation: The two 1x2 submatrices, plus the two 2x1 submatrices, plus the 2x2 submatrix.
Example 3:
Input: matrix = [[904]], target = 0 Output: 0
Constraints:
1 <= matrix.length <= 100
1 <= matrix[0].length <= 100
-1000 <= matrix[i][j] <= 1000
-10^8 <= target <= 10^8