Two Sum

Problem

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

 

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]

 

Constraints:

• 2 <= nums.length <= 104
• -109 <= nums[i] <= 109
• -109 <= target <= 109
• Only one valid answer exists.

Solution

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    let map = {};
    for (let i = 0; i < nums.length; ++i) {
        const t = target - nums[i];
        if (t in map) {
            return [i, map[t]];
        } else {
            map[nums[i]] = i;
        }
    }
};

Iterate through numbers while keeping track of which values have gone by using a map (where the key is the number and the value is the index of the number). If target minus the current number is in map, this means the two values sum up to target. Thus, we can return the current index and the corresponding index saved in map.