1. Two Sum

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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.

给一个整数数组，给一个数字，返回数组中两个数字的序号，这两个数字加起来等于给定数字。

假设每个输入只有一个确定的解。

Example:

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

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

public class Solution {    public int[] twoSum(int[] nums, int target) {        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();        int len = nums.length;        int[] defaultResult ={0,0};        for(int i = 0; i < len; i++){            if(map.get(target-nums[i]) != null){                int[] result = {map.get(target-nums[i]), i};                return result;            }            map.put(nums[i], i);        }        return defaultResult;    }}

new一个HashMap，得到数组长度，初始化结果。

给定数字减数组中数字，其结果没在map中，就加入map。有就返回两个数字的序号。

HashMap中是key-value，对此题目，数字作为key，序号为value

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