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].

思路：

在找的过程中建立索引，故一个循环可以求出解（总是使用未使用元素查找使用元素，可以保证每一对都能被检索到）

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> m = new HashMap<Integer, Integer>();
        for(int i=0;i<nums.length;i++){
            int num=target-nums[i];
            if(m.containsKey(num))
                return new int[]{m.get(num),i};
            m.put(nums[i],i);
        }
        throw null;
    }
}

Status	Runtime	Language
Accepted	8ms	java