001-Two-Sum.js

/**
 * https://leetcode.com/problems/two-sum/description/
 * Difficulty:Easy
 *
 * 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[]} numbers
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function (numbers, target) {

    for (var i = 0; i < numbers.length - 1; i++) {
        for (var j = i + 1; j < numbers.length; j++) {
            if (numbers[i] + numbers[j] === target) return [i, j];
        }
    }
};

var twoSum2 = function (numbers, target) {
    var map = {};
    for (var i = 0; i < numbers.length; i++) {
        var n = numbers[i];
        if (map[target - n] !== undefined) {
            return [map[target - n], i];
        } else {
            map[n] = i;
        }
    }
};

console.log(twoSum([2, 11, 15, 7], 9));
console.log(twoSum2([2, 7, 11, 15], 9));
console.log(twoSum2([2, 7, 11, 15], 26));
console.log(twoSum2([2, 7, 11, 15], 26));