Add solution #528

Author: JoshCrozier

README.md

@@ -423,6 +423,7 @@
 524|[Longest Word in Dictionary through Deleting](./0524-longest-word-in-dictionary-through-deleting.js)|Medium|
 525|[Contiguous Array](./0525-contiguous-array.js)|Medium|
 526|[Beautiful Arrangement](./0526-beautiful-arrangement.js)|Medium|
+528|[Random Pick with Weight](./0528-random-pick-with-weight.js)|Medium|
 530|[Minimum Absolute Difference in BST](./0530-minimum-absolute-difference-in-bst.js)|Easy|
 541|[Reverse String II](./0541-reverse-string-ii.js)|Easy|
 542|[01 Matrix](./0542-01-matrix.js)|Medium|

solutions/0528-random-pick-with-weight.js

@@ -0,0 +1,46 @@
+/**
+ * 528. Random Pick with Weight
+ * https://leetcode.com/problems/random-pick-with-weight/
+ * Difficulty: Medium
+ *
+ * You are given a 0-indexed array of positive integers w where w[i] describes the
+ * weight of the ith index.
+ *
+ * You need to implement the function pickIndex(), which randomly picks an index in
+ * the range [0, w.length - 1] (inclusive) and returns it. The probability of picking
+ * an index i is w[i] / sum(w).
+ *
+ * For example, if w = [1, 3], the probability of picking index 0 is 1 / (1 + 3) = 0.25
+ * (i.e., 25%), and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e., 75%).
+ */
+
+/**
+ * @param {number[]} w
+ */
+var Solution = function(w) {
+  this.sums = [];
+  let sum = 0;
+  for (const weight of w) {
+    sum += weight;
+    this.sums.push(sum);
+  }
+  this.total = sum;
+};
+
+/**
+ * @return {number}
+ */
+Solution.prototype.pickIndex = function() {
+  const target = Math.random() * this.total;
+  let left = 0;
+  let right = this.sums.length - 1;
+  while (left < right) {
+    const mid = Math.floor((left + right) / 2);
+    if (this.sums[mid] <= target) {
+      left = mid + 1;
+    } else {
+      right = mid;
+    }
+  }
+  return left;
+};