[LeetCode][Java] Two Sum

题目：

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9

Output: index1=1, index2=2

题意：

给定一个数组，挑出两个数，他们的和为目标值，返回这两个数在数组中的标号，并且保证index1 比index2 小。

假设一只有组解满足条件。注意返回的结果（index1 和index2）都不是从0 开始的。

算法分析：

利用HashMap,键(Key)存储数组中的数字值，值(value)存储该数字值的在数组中的标号.

假设先将两个数中较大的数(numbers[i])存储在map中，之后在数组标号（0~i）中搜寻（target-numbers[i]）,找到后返回标号。

代码如下：

import java.util.Hashtable;
import java.util.Iterator;
public class Solution
{
public int[] twoSum(int[] numbers, int target)
{
int num = numbers.length;
int index[] = new int[2];
HashMap <Integer,Integer> map = new HashMap<Integer,Integer>();
for(int i=0;i<num;i++)
{
if(!map.containsKey(numbers[i]))
map.put(numbers[i],i);

Integer temp = map.get(target-numbers[i]);
if(temp!=null && temp<i)
{
index[0]=temp+1;
index[1]=i+1;
}
}

return index;
}
}