Create Range Sum Query 2D - Mutable.js

Author: paopao2

Range Sum Query 2D - Mutable.js

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+/**
+Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2).
+
+Range Sum Query 2D
+The above rectangle (with the red border) is defined by (row1, col1) = (2, 1) and (row2, col2) = (4, 3), which contains sum = 8.
+
+Example:
+
+Given matrix = [
+  [3, 0, 1, 4, 2],
+  [5, 6, 3, 2, 1],
+  [1, 2, 0, 1, 5],
+  [4, 1, 0, 1, 7],
+  [1, 0, 3, 0, 5]
+]
+
+sumRegion(2, 1, 4, 3) -> 8
+update(3, 2, 2)
+sumRegion(2, 1, 4, 3) -> 10
+
+Note:
+
+    The matrix is only modifiable by the update function.
+    You may assume the number of calls to update and sumRegion function is distributed evenly.
+    You may assume that row1 ≤ row2 and col1 ≤ col2.
+
+*/
+/**
+ * @constructor
+ * @param {number[][]} matrix
+ */
+var NumMatrix = function(matrix) {
+    this.matrix = matrix;
+    this.rowLen = matrix.length;
+    this.colLen = this.rowLen === 0 ? 0 : matrix[0].length;
+    this.colSum = []; // colSum[i][j] means column sum from matrix[0][j] to matrix[i][j]
+    
+    for (let i = 0; i < this.rowLen; i++) {
+        this.colSum.push(new Array(this.colLen).fill(0));
+    }
+    
+    for (let i = 0; i < this.rowLen; i++) {
+        for (let j = 0; j < this.colLen; j++) {
+            if (i === 0) {
+                this.colSum[i][j] = this.matrix[i][j];
+            } else {
+                this.colSum[i][j] = this.matrix[i][j] + this.colSum[i - 1][j];
+            }
+        }
+    }
+};
+
+/**
+ * @param {number} row
+ * @param {number} col
+ * @param {number} val
+ * @return {void}
+ */
+NumMatrix.prototype.update = function(row, col, val) {
+    for (let i = row; i < this.rowLen; i++) {
+        this.colSum[i][col] += val - this.matrix[row][col];
+    }
+    
+    this.matrix[row][col] = val;
+};
+
+/**
+ * @param {number} row1
+ * @param {number} col1
+ * @param {number} row2
+ * @param {number} col2
+ * @return {number}
+ */
+NumMatrix.prototype.sumRegion = function(row1, col1, row2, col2) {
+    let result = 0;
+    
+    for (let i = col1; i <= col2; i++) {
+        if (row1 === 0) {
+            result += this.colSum[row2][i];
+        } else {
+            result += this.colSum[row2][i] - this.colSum[row1 - 1][i];
+        }
+    }
+    
+    return result;
+};
+
+
+/**
+ * Your NumMatrix object will be instantiated and called as such:
+ * var numMatrix = new NumMatrix(matrix);
+ * numMatrix.sumRegion(0, 1, 2, 3);
+ * numMatrix.update(1, 1, 10);
+ * numMatrix.sumRegion(1, 2, 3, 4);
+ */