LeetCode in Kotlin
1074. Number of Submatrices That Sum to Target
Hard
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 <= 1001 <= matrix[0].length <= 100-1000 <= matrix[i] <= 1000-10^8 <= target <= 10^8
Solution
class Solution {
fun numSubmatrixSumTarget(matrix: Array<IntArray>, target: Int): Int {
val rows = matrix.size
val columns = matrix[0].size
for (i in 0 until rows) {
for (j in 1 until columns) {
matrix[i][j] += matrix[i][j - 1]
}
}
val sumMap: HashMap<Int, Int> = HashMap()
var cur: Int
var res = 0
for (i in 0 until columns) {
for (j in i until columns) {
sumMap.clear()
sumMap[0] = 1
cur = 0
for (ints in matrix) {
cur += ints[j] - if (i > 0) ints[i - 1] else 0
res += sumMap.getOrDefault(cur - target, 0)
sumMap[cur] = sumMap.getOrDefault(cur, 0) + 1
}
}
}
return res
}
}