Map Sum Pairs in JavaScript

Problem

We are required to implement a MapSum class with insert, and sum methods. For the method insert, we'll be given a pair of (string, integer). The string represents the key and the integer represents the value. If the key already existed, then the original key-value pair will be overridden to the new one.

For the method sum, we'll be given a string representing the prefix, and we need to return the sum of all the pairs' values whose key starts with the prefix.

Example

Following is the code −

 Live Demo

class Node {
   constructor(val) {
      this.num = 0
      this.val = val
      this.children = {}
   }
}
class MapSum {
   constructor(){
      this.root = new Node('');
   }
}
MapSum.prototype.insert = function (key, val) {
   let node = this.root
   for (const char of key) {
      if (!node.children[char]) {
         node.children[char] = new Node(char)
      }
      node = node.children[char]
   }
   node.num = val
}

MapSum.prototype.sum = function (prefix) {
   let sum = 0
   let node = this.root
   for (const char of prefix) {
      if (!node.children[char]) {
         return 0
      }
      node = node.children[char]
   }
   const helper = (node) => {
      sum += node.num
      const { children } = node
      Object.keys(children).forEach((key) => {
         helper(children[key])
      })
   }
   helper(node)
   return sum
}
const m = new MapSum();
console.log(m.insert('apple', 3));
console.log(m.sum('ap'));

Output

undefined
3