# Sales by Match solution in Javascript

## Problem: There is a large pile of socks that must be paired by color. Given an array of integers representing the color of each sock, determine how many pairs of socks with matching colors there are.
Example
n = 7,
ar = [1,2,1,2,1,3,2]

There is one pair of color 1 and one of color 2. There are three odd socks left, one of each color. The number of pairs is 2.

Function Description

Complete the sockMerchant function in the editor below.

sockMerchant has the following parameter(s):

int n: the number of socks in the pile
int ar[n]: the colors of each sock

Returns

int: the number of pairs

## Solution:

The simplest way to solve this problem is by breaking it down into simple steps as follows:

1. Go through the list of items and sort them by color.
2. Once we have a collection of items of the same color, we can determine from the collection how many form a pair.

In Javascript we solve that in the following:

1. Loop through the array and assign unique values to a map. If a value already exists in the map, we will increment the value. The idea is to have a map that shows items and the number of times it appears.

`Map(4) { 10 => 4, 20 => 3, 30 => 1, 50 => 1 }`

1. From the map, we can now detemine which forms a pair.
``````function sockMerchant(n, ar) {

//1. Loop through array items and arrange items in a map by unique color

let mapOfColors = new Map();

for(let i = 0; i< n ; i++ ){
// If found, increment the map value
if(mapOfColors.has(ar[i])){
let currentVal = mapOfColors.get(ar[i]);
mapOfColors.set(ar[i], currentVal+1);
}
else{
mapOfColors.set(ar[i], 1)
}
}

//2. From the map, we can now detemine which form a pair

let pairs = 0;

for(let countOfColor of mapOfColors.values() ){
// Check if it can create complete pairs
if(countOfColor % 2 === 0){
pairs += countOfColor/2;
}else{
pairs += (countOfColor-1)/2;
}
}

return pairs;
}

const pairs = sockMerchant(9, [10, 20, 20, 10, 10, 30, 50, 10, 20]);
console.log ( pairs);
`````` 