LeetCode ---2.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].

网址来源：https://leetcode.com/problems/two-sum/#/description

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[i] + nums[j] == target) {
                    return new int[]{i, j};
                }
            }
        }
        throw new IllegalArgumentException("No solution");
    }

解题思路：通过2层循环来找出某2个值的和是否等于target的值，若相等则返回该2个值的索引下标，关键点在于第二层循环的j=i+1,减少遍历的重复以及降低时间复杂度