1. Two Sum

题目：

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].

 

复杂度：

时间：O(n^2)、空间：O(1)

 

实现：

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        for(int first = 0; first < nums.length; ++first) {
            for(int second = first + 1; second < nums.length; ++second) {
                if(nums[first] + nums[second] == target) {
                    return new int[] { first, second };
                }
            }
        }
        
        return new int[0];
    }
}