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

Added solution for range-sum-query-2d-immutable in JS

Author: aadil42

Diff for: javascript/0304-range-sum-query-2d-immutable.js

@@ -0,0 +1,33 @@
+/**
+ * https://leetcode.com/problems/range-sum-query-2d-immutable/
+ * @param {number[][]} matrix
+ */
+ var NumMatrix = function(matrix) {
+    this.matrix = matrix;
+};
+
+/** 
+ * 
+ * m = row2 - row1; n = col2 - col1
+ * Time O(m*n) | Space O(1)
+ * @param {number} row1 
+ * @param {number} col1 
+ * @param {number} row2 
+ * @param {number} col2
+ * @return {number}
+ */
+NumMatrix.prototype.sumRegion = function(row1, col1, row2, col2) {
+    let sum = 0;
+    for(let i = row1; i < row2 + 1; i++) {
+        for(let j = col1; j < col2 + 1; j++) {
+            sum += this.matrix[i][j];
+        }
+    }
+    return sum;
+};
+
+/** 
+ * Your NumMatrix object will be instantiated and called as such:
+ * var obj = new NumMatrix(matrix)
+ * var param_1 = obj.sumRegion(row1,col1,row2,col2)
+ */