【2】1. Two Sum

转载于 2017-02-02 08:03:00 发布 · 42 阅读

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原文链接：http://www.cnblogs.com/93scarlett/p/6360886.html

本文介绍了一个经典的编程面试题——TwoSum问题。通过使用哈希表的方法，在O(n)的时间复杂度内找到数组中两个数相加等于特定目标值的下标。文章提供了完整的C++实现代码。

1. Two Sum

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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].

 1 class Solution {
 2 public:
 3     vector<int> twoSum(vector<int>& nums, int target) {
 4         unordered_map<int, int> hash;
 5         vector<int> result;
 6         for(int i = 0; i < nums.size(); i++){
 7             if(hash.find(target - nums[i]) != hash.end()){
 8                 result.push_back(hash[target - nums[i]]);
 9                 result.push_back(i);
10                 return result;
11             }
12             hash[nums[i]] = i;
13         }
14         result.push_back(-1);
15         result.push_back(-1);
16         return result;
17     }
18 };