Add solution #307

Author: JoshCrozier

README.md

@@ -250,6 +250,7 @@
 303|[Range Sum Query - Immutable](./0303-range-sum-query-immutable.js)|Easy|
 304|[Range Sum Query 2D - Immutable](./0304-range-sum-query-2d-immutable.js)|Medium|
 306|[Additive Number](./0306-additive-number.js)|Medium|
+307|[Range Sum Query - Mutable](./0307-range-sum-query-mutable.js)|Medium|
 309|[Best Time to Buy and Sell Stock with Cooldown](./0309-best-time-to-buy-and-sell-stock-with-cooldown.js)|Medium|
 315|[Count of Smaller Numbers After Self](./0315-count-of-smaller-numbers-after-self.js)|Hard|
 316|[Remove Duplicate Letters](./0316-remove-duplicate-letters.js)|Medium|

solutions/0307-range-sum-query-mutable.js

@@ -0,0 +1,78 @@
+/**
+ * 307. Range Sum Query - Mutable
+ * https://leetcode.com/problems/range-sum-query-mutable/
+ * Difficulty: Medium
+ *
+ * Given an integer array nums, handle multiple queries of the following types:
+ * 1. Update the value of an element in nums.
+ * 2. Calculate the sum of the elements of nums between indices left and right inclusive
+ *    where left <= right.
+ *
+ * Implement the NumArray class:
+ * - NumArray(int[] nums) Initializes the object with the integer array nums.
+ * - void update(int index, int val) Updates the value of nums[index] to be val.
+ * - int sumRange(int left, int right) Returns the sum of the elements of nums between
+ *   indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]).
+ */
+
+/**
+ * @param {number[]} nums
+ */
+var NumArray = function(nums) {
+  this.n = nums.length;
+  this.tree = new Array(2 * this.n);
+
+  for (let i = 0; i < this.n; i++) {
+    this.tree[this.n + i] = nums[i];
+  }
+
+  for (let i = this.n - 1; i > 0; i--) {
+    this.tree[i] = this.tree[i * 2] + this.tree[i * 2 + 1];
+  }
+};
+
+/**
+ * @param {number} index
+ * @param {number} val
+ * @return {void}
+ */
+NumArray.prototype.update = function(index, val) {
+  let position = this.n + index;
+  this.tree[position] = val;
+
+  while (position) {
+    let left = position;
+    let right = position;
+    if (position % 2 === 0) {
+      right = position + 1;
+    } else {
+      left = position - 1;
+    }
+    this.tree[position >> 1] = this.tree[left] + this.tree[right];
+    position >>= 1;
+  }
+};
+
+/**
+ * @param {number} left
+ * @param {number} right
+ * @return {number}
+ */
+NumArray.prototype.sumRange = function(left, right) {
+  let sum = 0;
+  let l = this.n + left;
+  let r = this.n + right + 1;
+
+  while (l < r) {
+    if (l % 2 == 1) {
+      sum += this.tree[l++];
+    }
+    if (r % 2 == 1) {
+      sum += this.tree[--r];
+    }
+    l >>= 1;
+    r >>= 1;
+  }
+
+  return sum;
+};