【LeetCode Easy】001 Two Sum

Easy 001 Two Sum

Description:

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].

My Solution:

Fast Solution One:

Fast Solution Two: