Two Sum —— Leetcode

最新推荐文章于 2021-11-21 16:19:23 发布

BlitzSkies

最新推荐文章于 2021-11-21 16:19:23 发布

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分类专栏： Leetcode

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本文介绍了一种使用哈希表解决两数之和问题的方法。给定一个整数数组及目标值，通过哈希表快速查找数组中两个数是否能相加得到目标值，并返回这两个数的下标。

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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

用hashtable解决和为target的问题。

源码不太美观，还是搜一下leetcode上votes最高的答案吧。

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        std::unordered_map<int, int> m;
        vector<int> res;
        
        for(int i=0; i<nums.size(); ++i) {
            if(m[nums[i]] == 0)
                m[nums[i]] = i+1;
        }
        
        int tmp = 0;
        for(int j=0; j<nums.size(); ++j) {
            tmp = m[target-nums[j]];
            if(tmp > 0) {
                if(tmp != j+1) {
                    res.push_back(min(tmp, j+1));
                    res.push_back(max(tmp,j+1));
                    break;
                }
            }
        }
        
        return res;
    }
};