1. Two Sum

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.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

把待获取的另外一个值放到Set里面，每一次就判断Set里面里面也没有这个另外一个带获取的值

public class Solution {    public int[] twoSum(int[] nums, int target) {                Map<Integer, Integer> map = new HashMap<Integer, Integer>();        int[]rst = new int[2];        int cnt = 0;                for(int i=0; i<nums.length; i++) {            if(map.containsKey(nums[i])) {                rst[0] = map.get(nums[i]);                rst[1] = i;                return rst;            }            map.put(target-nums[i], i);           }        return rst;    }}