LeetCode 1、Two Sum

转载于 2017-02-25 21:21:00 发布 · 49 阅读

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/clairvoyant/p/6442891.html

本文介绍了一种解决两数之和问题的有效方法。通过使用哈希表存储目标值与数组元素之间的差值及其索引，可以快速找到两个加起来等于特定目标值的数的索引。这种方法仅需遍历一次数组，提高了效率。

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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].

https://leetcode.com/problems/two-sum/?tab=Description

Hash。

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        
        vector<int> result;
        map<int, int> hash;
        
        for (int i = 0; i < nums.size(); ++i) {
            if (hash.count(nums[i]) != 0) {
                result.push_back(hash[nums[i]]);
                result.push_back(i);
                break;
            }
            hash[target - nums[i]] = i;
        }
        return result;
    }
};