Create 1074-number-of-submatrices-that-sum-to-target.kt

Author: a93a

kotlin/1074-number-of-submatrices-that-sum-to-target.kt

@@ -0,0 +1,32 @@
+class Solution {
+    fun numSubmatrixSumTarget(matrix: Array<IntArray>, target: Int): Int {
+        val n = matrix.size
+        val m = matrix[0].size
+        val prefix = Array (n) { IntArray (m) }
+
+        for (i in 0 until n) {
+            for (j in 0 until m) {
+                val top = if (i > 0) prefix[i - 1][j] else 0
+                val left = if (j > 0) prefix[i][j - 1] else 0
+                val topLeft = if (minOf(i, j) > 0) prefix[i - 1][j - 1] else 0
+                prefix[i][j] = matrix[i][j] + top + left - topLeft
+            }
+        }
+
+        var res = 0
+        for (i in 0 until n) {
+            for (i2 in i until n) {
+                var count = HashMap<Int, Int>()
+                count[0] = 1
+                for (j in 0 until m) {
+                    val curSum = prefix[i2][j] - (if (i > 0) prefix[i - 1][j] else 0)
+                    val diff = curSum - target
+                    res += (count[diff] ?: 0)
+                    count[curSum] = (count[curSum] ?: 0) + 1
+                }
+            }
+        }
+
+        return res
+    }
+}