Leetcode 128 Longest Consecutive Sequence

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.

找出最大连续的序列长度。

用STL快又简单，道理我懂，但是这题初衷应该是让我们用并查集做，虽然这会烦一些慢一些。

好久没写并查集，有点生疏

代码语言：javascript复制

class Solution {
public:
    int find(int x,unordered_map<int,int> &set)//引用不需要拷贝到函数空间，事实证明引用比传值快
    {
        if(set[x]!=x)
        set[x]=find(set[x],set);
        return set[x];
    }
    int longestConsecutive(vector<int>& nums) {
        int res=1;
        if(nums.empty()) return 0;
        unordered_map<int,int> set,dp;
        for(int i=0;i<nums.size();i  )
        {
            set[nums[i]]=nums[i];
            dp[nums[i]]=1;
        }
        for(int i=0;i<nums.size();i  )
        {
            int y,x=find(nums[i],set);
            if(set.find(nums[i]-1)!=set.end())
            {
                y=find(nums[i]-1,set);
                if(y!=x)
                {
                    dp[x] =dp[y];
                    set[y]=x;
                }
                res=max(res,dp[x]);
            }
            if(set.find(nums[i] 1)!=set.end())
            {
                y=find(nums[i] 1,set);
                if(y!=x)
                {
                    dp[x] =dp[y];
                    set[y]=x;
                }
                res=max(res,dp[x]);
            }
        }
        return res;
    }
};

algorithm sequence stl

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