Description 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.

Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity? Solutions Solution 1: Hash Table We can use a hash table d to store each element and its corresponding index.

Traverse the array nums , for the current element nums [ i ] , we first check if target − nums [ i ] is in the hash table d . If it is in d , it means the target value has been found, and we return the indices of target − nums [ i ] and i .

Time complexity is O ( n ) , and space complexity is O ( n ) , where n is the length of the array nums .