Two sum

TwoSum

给定一个整数数组，返回两个数字的索引，使它们相加等于一个特定的目标。
您可以假设每个输入都一个解决方案，而你可能不会使用相同元素两次

例如：

Given nums = [2, 7, 11, 15], target = 9,

Because nums[**0**] + nums[**1**] = 2 + 7 = 9,
return [**0**, **1**].

The brute force approach is simple. Loop through each element xx and find if there is another value that equals to target - xtarget−x.

public int[] twoSum(int[] nums, int target) {
    for (int i = 0; i < nums.length; i++) {
        for (int j = i + 1; j < nums.length; j++) {
            if (nums[j] == target - nums[i]) {
                return new int[] { i, j };
            }
        }
    }
    throw new IllegalArgumentException("No two sum solution");
}