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

解题思路

使用暴力求解。时间复杂度O(n^2)，空间复杂度O(1)。

使用hash表存储访问过的数。时间复杂度O(n)，空间复杂度O(n)。（√）

代码

int[] twoSum(int[] nums, int target ){
		
		HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
		int[] index=new int[2];

		for(int i=0;;i++){
			if(hm.containsKey(target-nums[i])){
				index[0] = hm.get(target-nums[i])+1;
				index[1] = i+1;
				break;
			}
			else{
				hm.put(nums[i],i);
			}
		}
		
		return index;	
	}

运行结果

1.Two Sum

原文：http://blog.csdn.net/hiboy_111/article/details/47691431