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

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)
+ */