Question:

Given an array of integers, returnindicesof 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 thesameelement twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0,1].

Answer:

- method 1

note: this is more obvious, but less efficient;

- method 2

note: using a new object makes the code more efficient with only one loop~~