随机练习题Leetcode（一）

最新推荐文章于 2025-04-09 21:53:03 发布

JaneStupid

最新推荐文章于 2025-04-09 21:53:03 发布

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分类专栏： C++ 文章标签： leetcode

本文链接：https://blog.youkuaiyun.com/sinat_31655507/article/details/54342356

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本文介绍了三种不同的两数之和问题的算法解决方案，包括使用哈希表进行快速查找、针对已排序数组采用二分搜索法提高效率以及设计数据结构支持实时插入与查找操作。

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1. Two Sum

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        multimap<int, int> map1;
        for (int i =0 ; i<nums.size(); i++)
            //map1[nums[i]]=i;
            map1.insert(std::pair<int,int>(nums[i],i));

        vector<int> ret;
        if(!map1.empty())
        {
            multimap<int, int>::iterator iter = map1.begin();
            for(; iter!=map1.end(); iter++)
            {
                int first = (*iter).first;
                multimap<int, int>::iterator iter2 = map1.find(target-first);
                if(iter2!=map1.end() && iter2!=iter)
                {
                    ret.push_back((*iter).second);
                    ret.push_back((*iter2).second);
                    break;
                }
            }
        }
        return ret;
    }
};
/*
注释：
1.所给序列可能有重复的元素
2.在查找时，需要保证查找到的不是同一个元素的迭代器
*/

167. Two Sum II - Input array is sorted

class Solution {
public:
    vector<int> twoSum(vector<int>& numbers, int target) {
        vector<int> ret;
        for(int i = 0; i<numbers.size(); i++)
        {
            int first = numbers[i];
            int second = BinarySearch(numbers, i+1, numbers.size(), target-first);
            if(second!=-1 && second>i)
            {
                ret.push_back(i+1);
                ret.push_back(second+1);
                break;
            }
        }
        return ret;
    }
    int BinarySearch(vector<int> &num, int start, int end, int target)
    {
        while(start<=end)
        {
            int mid = start+(end-start)/2;
            if(target < num[mid])
                end = mid - 1;
            if(target > num[mid]) 
                start = mid + 1;
            if(target == num[mid])
                return mid;
            return BinarySearch(num, start, end, target);
        }
        return -1;
    }
};

170. Two Sum III - Data structure design

class TwoSum {
public:
    // Add the number to an internal data structure.
    void add(int number) {
        numbers[number]++;
    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    bool find(int value) {
        for(auto iter: numbers)
        {
            if(numbers.find(value- iter.first)!=numbers.end())
            {
                if(value - iter.first == iter.first)
                {
                    if(iter.second>1)
                        return true;
                }
                else
                    return true;
            }
        }
        return false;
    }

private:
    //vector<int> numbers;
    unordered_map<int, int> numbers;
};

// Your TwoSum object will be instantiated and called as such:
// TwoSum twoSum;
// twoSum.add(number);
// twoSum.find(value);