two-sum.js

// 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]
// Output: 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 <= 103
// -109 <= nums[i] <= 109
// -109 <= target <= 109
// Only one valid answer exists.

 const twoSum = function(nums, target) {
    const comp = {};
    for(let i=0; i<nums.length; i++){
        if(comp[nums[i] ]>=0){
            return [ comp[nums[i] ] , i]
        }
        comp[target-nums[i]] = i
    }
};




var twoSum = function(nums, target){
    const prevValues = {}
    for (let i = 0; i < nums.length; i++){
        const currentNumber = nums[i]
        const neededValue = target - currentNumber
        const index2 = prevValues[neededValue]
        if (index2 != null){
            return [index2, i]
        } else {
            prevValues[currentNumber] = i
        }
    }
}