Create 0304-range-sum-query-2d-immutable.kt

Author: a93a

kotlin/0304-range-sum-query-2d-immutable.kt

@@ -0,0 +1,39 @@
+class NumMatrix(matrix: Array<IntArray>) {
+
+    val row = matrix.size
+    val col = matrix[0].size
+    val prefixSum = Array(row + 1){ IntArray(col + 1) }
+
+    init {
+        for(i in 0 until row) {
+            var prefix = 0
+            for(j in 0 until col) {
+                println("i: $i j: $j")
+                prefix += matrix[i][j]
+                prefixSum[i + 1][j + 1] = prefix + prefixSum[i][j + 1]
+            }
+        }
+    }
+    
+
+    fun sumRegion(row1: Int, col1: Int, row2: Int, col2: Int): Int {
+        val r1 = row1 + 1
+        val r2 = row2 + 1
+        val c1 = col1 + 1
+        val c2 = col2 + 1
+
+        val botRight = prefixSum[r2][c2]
+        val aboveOf = prefixSum[r1 - 1][c2]
+        val leftOf = prefixSum[r2][c1 - 1]
+        val topLeft = prefixSum[r1 - 1][c1 - 1]
+
+        return botRight - aboveOf - leftOf + topLeft
+    }
+
+}
+
+/**
+ * Your NumMatrix object will be instantiated and called as such:
+ * var obj = NumMatrix(matrix)
+ * var param_1 = obj.sumRegion(row1,col1,row2,col2)
+ */