Time Based Key-Value Store

Time Based Key-Value Store - LeetCodeLeetCode

Problem

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 "".

Example 1:

Input
["TimeMap", "set", "get", "get", "set", "get", "get"]
[[], ["foo", "bar", 1], ["foo", 1], ["foo", 3], ["foo", "bar2", 4], ["foo", 4], ["foo", 5]]
Output
[null, null, "bar", "bar", null, "bar2", "bar2"]
Explanation
TimeMap timeMap = new TimeMap();
timeMap.set("foo", "bar", 1);  // store the key "foo" and value "bar" along with timestamp = 1.
timeMap.get("foo", 1);         // return "bar"
timeMap.get("foo", 3);         // return "bar", since there is no value corresponding to foo at timestamp 3 and timestamp 2, then the only value is at timestamp 1 is "bar".
timeMap.set("foo", "bar2", 4); // store the key "foo" and value "bar2" along with timestamp = 4.
timeMap.get("foo", 4);         // return "bar2"
timeMap.get("foo", 5);         // return "bar2"

Pseudocode

- don't understand code, please review

Solution

var TimeMap = function () {
  this.map = new Map();
};

/**
 * @param {string} key
 * @param {string} value
 * @param {number} timestamp
 * @return {void}
 */
TimeMap.prototype.set = function (key, value, timestamp) {
  if (!this.map.has(key)) {
    this.map.set(key, []);
  }

  this.map.get(key).push([timestamp, value]);
};

/**
 * @param {string} key
 * @param {number} timestamp
 * @return {string}
 */
TimeMap.prototype.get = function (key, timestamp) {
  if (!this.map.has(key)) {
    return "";
  }

  if (timestamp < this.map.get(key)[0][0]) {
    return "";
  }

  let left = 0;
  let right = this.map.get(key).length;

  while (left < right) {
    const mid = Math.floor((left + right) / 2);

    if (this.map.get(key)[mid][0] <= timestamp) {
      left = mid + 1;
    } else {
      right = mid;
    }
  }

  if (right > left) {
    return "";
  }

  return this.map.get(key)[right - 1][1];
};

/**
 * Your TimeMap object will be instantiated and called as such:
 * var obj = new TimeMap()
 * obj.set(key,value,timestamp)
 * var param_2 = obj.get(key,timestamp)
 */

Time and Space Complexity

Time

• What did the code do

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Space

• What did the code do

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