第一题，Two Sum

此题给定一个数组和目标target，求两个数之和等于target，返回这两个数的下标位置

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]

经典解法就是双循环数组，遇到相等的直接返回即可（无重复答案）

    public int[] twoSum(int[] nums, int target) {
        int len = nums.length;
        for(int i = 0; i < len; i ++)
            for(int j = i+ 1; j < len; j++)
            {
                if (nums[i] + nums[j] == target)
                    return new int[]{i,j};
            }
        return new int[]{-1,-1};

    }

需要注意的点

1、j从i+1开始，不要再从1开始循环了

2、直接返回new int[]{i,j}，这种方式可以学习一下，作为java生成数组的一种方式