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.

 Notice

You may assume that each input would have exactly one solution

Have you met this question in a real interview? 

Yes

Example

numbers=[2, 7, 11, 15], target=9

return [1, 2]

Either of the following solutions are acceptable:

• O(n) Space, O(nlogn) Time
• O(n) Space, O(n) Time

 

LeetCode上的原题，请参见我之前的博客。

 

class Solution {public:    /*     * @param numbers : An array of Integer     * @param target : target = numbers[index1] + numbers[index2]     * @return : [index1+1, index2+1] (index1 < index2)     */    vector
     
       twoSum(vector
      
        &nums, int target) {        unordered_map
       
         m;        for (int i = 0; i < nums.size(); ++i) m[nums[i]] = i;        for (int i = 0; i < nums.size(); ++i) {            int t = target - nums[i];            if (m.count(t) && m[t] != i) {                return {i + 1, m[t] + 1};            }        }        return {};    }};