# Map Sum Pairs in JavaScript

JavascriptWeb DevelopmentFront End Technology

## 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
Published on 24-Apr-2021 10:27:08