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].
暴力解法（Java）：
1 class Solution { 2 public int[] twoSum(int[] nums, int target) { 3 for(int i=0;i<nums.length;i++) 4 for(int j=i+1;j<nums.length;j++) 5 if(nums[i]+nums[j]==target) 6 return new int[]{i,j}; 7 return new int[]{0,0}; 8 } 9 }
利用hashset，遍历nums，若在set中找到一个值与当前值相加为target，则返回两个下标，否则将当前值加入set（Java）：
class Solution { public int[] twoSum(int[] nums, int target) { Set<Integer> set = new HashSet<>(); int i=0; int j=0; for(i=0;i<nums.length;i++) { if(set.contains(target-nums[i])) break; else set.add(nums[i]); } while(nums[j]!=target-nums[i]) j++; return new int[]{j,i}; } }
原文：https://www.cnblogs.com/trymorel/p/12520917.html