1. Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

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

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

/**

* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var twoSum = function(nums, target) {
    const dict = Object.create(null);
    const find = [];
    for (let i = 0; i < nums.length; i++) {
        if (dict[target - nums[i]] !== undefined) {
            find.push(dict[target - nums[i]]);
            find.push(i);
            return find;
        }
        dict[nums[i]] = i;
    }
}