Longest Consecutive Sequence

最新推荐文章于 2025-03-19 23:17:40 发布

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最新推荐文章于 2025-03-19 23:17:40 发布

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原文链接：http://www.cnblogs.com/pengpenghappy/p/3864157.html

本文介绍了一种寻找整数数组中最长连续元素序列的算法，并提供了一个C++实现示例。该算法的时间复杂度为O(n)，通过使用哈希表记录每个元素的状态来达到线性时间内的查找效率。

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

    map<int, int> mp;

    int longestConsecutive(vector<int> &num) 
    {
        int i;
        // map all the numbers and set value to 1 (not accessed state)
        for (i = 0; i < num.size(); i++)
        {
            mp[num[i]] = 1;
        }

        int res = 0;
        for (i = 0; i<num.size(); i++){
            int sum = 1;
            if (mp.count(num[i]))
            {
                mp[num[i]] = 0;
                int left = num[i] - 1;
                // if the left number exist in the map and not accessed
                while (mp.count(left) && mp[left] != 0)
                {
                    mp[left--] = 0;
                    sum++;
                }
                int right = num[i] + 1;
                // if the right member exist in the map and not accessed
                while (mp.count(right) && mp[right] != 0)
                {
                    mp[right++] = 0;
                    sum++;
                }
            }
            if (res<sum)
                res = sum;
        }
        return res;
    };

int _tmain(int argc, _TCHAR* argv[])
{
    Solution *sln = new Solution();
vector<int> svec;
    svec.push_back(100);
    svec.push_back(4);
    svec.push_back(200);
    svec.push_back(3);
    svec.push_back(101);
    svec.push_back(2);
    svec.push_back(3);
    svec.push_back(99);
    svec.push_back(2);
    svec.push_back(98);
    svec.push_back(96);
    svec.push_back(97);

    int ret = sln->longestConsecutive(svec);
    cout << ret << endl;

    return 0;
}