Add solution #981

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,063 LeetCode solutions in JavaScript
+# 1,064 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -789,6 +789,7 @@
 978|[Longest Turbulent Subarray](./solutions/0978-longest-turbulent-subarray.js)|Medium|
 979|[Distribute Coins in Binary Tree](./solutions/0979-distribute-coins-in-binary-tree.js)|Medium|
 980|[Unique Paths III](./solutions/0980-unique-paths-iii.js)|Hard|
+981|[Time Based Key-Value Store](./solutions/0981-time-based-key-value-store.js)|Medium|
 985|[Sum of Even Numbers After Queries](./solutions/0985-sum-of-even-numbers-after-queries.js)|Easy|
 989|[Add to Array-Form of Integer](./solutions/0989-add-to-array-form-of-integer.js)|Easy|
 994|[Rotting Oranges](./solutions/0994-rotting-oranges.js)|Medium|

solutions/0981-time-based-key-value-store.js

@@ -0,0 +1,54 @@
+/**
+ * 981. Time Based Key-Value Store
+ * https://leetcode.com/problems/time-based-key-value-store/
+ * Difficulty: Medium
+ *
+ * Design a time-based key-value data structure that can store multiple values for the same key
+ * at different time stamps and retrieve the key's value at a certain timestamp.
+ *
+ * Implement the TimeMap class:
+ * - TimeMap() Initializes the object of the data structure.
+ * - void set(String key, String value, int timestamp) Stores the key key with the value value
+ *   at the given time timestamp.
+ * - String get(String key, int timestamp) Returns a value such that set was called previously,
+ *   with timestamp_prev <= timestamp. If there are multiple such values, it returns the value
+ *   associated with the largest timestamp_prev. If there are no values, it returns "".
+ */
+
+var TimeMap = function() {
+  this.store = new Map();
+};
+
+/**
+ * @param {string} key
+ * @param {string} value
+ * @param {number} timestamp
+ * @return {void}
+ */
+TimeMap.prototype.set = function(key, value, timestamp) {
+  if (!this.store.has(key)) this.store.set(key, []);
+  this.store.get(key).push([timestamp, value]);
+};
+
+/**
+ * @param {string} key
+ * @param {number} timestamp
+ * @return {string}
+ */
+TimeMap.prototype.get = function(key, timestamp) {
+  if (!this.store.has(key)) return '';
+  const entries = this.store.get(key);
+  let left = 0;
+  let right = entries.length - 1;
+
+  while (left <= right) {
+    const mid = Math.floor((left + right) / 2);
+    const [midTime, midValue] = entries[mid];
+
+    if (midTime === timestamp) return midValue;
+    if (midTime < timestamp) left = mid + 1;
+    else right = mid - 1;
+  }
+
+  return right >= 0 ? entries[right][1] : '';
+};