LeetCode - Two Sum

最新推荐文章于 2021-12-23 23:38:17 发布

superzrx

最新推荐文章于 2021-12-23 23:38:17 发布

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本文链接：https://blog.youkuaiyun.com/superzrx/article/details/38778825

本文介绍了一种解决两数之和问题的有效算法。通过构建一个哈希表来记录数组中每个元素的位置，该方法能在O(n)的时间复杂度内找到两个数，使它们的和等于目标值。文章详细解释了算法的实现过程，并提供了完整的C++代码示例。

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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

使用hash表记录每个数值出现的位置

构建hash表需要O(n)的时间和空间

使用STL的map查找需要O(log(n)

class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        vector<int> ret;
        map<int,int> m;
        for(int i=0;i<numbers.size();i++){
            m[numbers[i]]=i;
        }
        for(int i=0;i<numbers.size();i++){
            if(m.find(target-numbers[i])!=m.end()){
                int ind=m[target-numbers[i]];
                if(ind!=i){
                    ret.push_back(i+1);
                    ret.push_back(m[target-numbers[i]]+1);
                    break;
                }
            }
        }
        return ret;
    }
};