561. Array Partition I

Description

Given an array of 2n integers, your task is to group these integers into n pairs of integer, say (a₁, b₁), (a₂, b₂), ..., (a_n, b_n) which makes sum of min(a_i, b_i) for all i from 1 to n as large as possible.

Example 1:

Input: [1,4,3,2]

Output: 4
Explanation: n is 2, and the maximum sum of pairs is 4 = min(1, 2) + min(3, 4).

Note:

1. n is a positive integer, which is in the range of [1, 10000].
2. All the integers in the array will be in the range of [-10000, 10000].

Solution

Solution 1

/**
 * Higher readability
 * @param {number[]} nums
 * @return {number}
 */
var arrayPairSum = function(nums) {
    "use strict";
    return nums.sort((a, b) => a-b)
        .filter((num, idx) => idx % 2 === 0)
        .reduce((sum, num) => sum + num, 0);
};

Solution 2

/**
 * More efficient
 * @param {number[]} nums
 * @return {number}
 */
var arrayPairSum = function(nums) {
    "use strict";
    nums.sort((a, b) => a-b);
    let sum = 0;
    for (let i = 0; i < nums.length; i += 2) {
        sum += nums[i];
    }
    return sum;
};