LeetCode-Longest Consecutive Sequence

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#leetcode #Longest Consecutive

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本文介绍了一种算法，用于在未排序的整数数组中找到最长的连续整数序列。通过使用哈希集合，该算法能够在O(n)复杂度内解决问题。

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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.

Solution:

Code:

<span style="font-size:14px;">class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        const int length = num.size();
        if (length == 0 || length == 1) return length;
        unordered_set<int> s;
        for (int i = 0; i < length; ++i)
            s.insert(num[i]);
        int result = 1, count, temp;
        for (int i = 0; i < length; ++i)
            if (s.find(num[i]) != s.end()) {
                temp = num[i];
                s.erase(temp);
                count = 1;
                while (s.find(temp-1) != s.end()) {
                    --temp;
                    ++count;
                    s.erase(temp);
                }
                temp = num[i];
                while (s.find(temp+1) != s.end()) {
                    ++temp;
                    ++count;
                    s.erase(temp);
                }
                result = max(result, count);
            }
        return result;
    }
};</span>