#677 - Map Sum Pairs

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Problem Description

Design a map that allows you to do the following:

Maps a string key to a given value.
Returns the sum of the values that have a key with a prefix equal to a given string.

Implement the MapSum class:

MapSum() Initializes the MapSum object.
void insert(String key, int val) Inserts the key-val pair into the map. If the key already existed, the original key-value pair will be overridden to the new one.
int sum(string prefix) Returns the sum of all the pairs' value whose key starts with the prefix.

Solution

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

/**
 * @param {string} key
 * @param {number} val
 * @return {void}
 */
MapSum.prototype.insert = function(key, val) {
  this.map.set(key, val);
};

/**
 * @param {string} prefix
 * @return {number}
 */
MapSum.prototype.sum = function(prefix) {
  return [...this.map.entries()].reduce((total, [key, val]) => {
    return key.startsWith(prefix) ? total + val : total;
  }, 0);
};