leetocde 85: Longest Consecutive Sequence

最新推荐文章于 2025-03-19 23:17:40 发布

xudli

最新推荐文章于 2025-03-19 23:17:40 发布

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本文链接：https://blog.youkuaiyun.com/xudli/article/details/8600923

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。该算法能在O(n)的时间复杂度内解决给定问题，通过使用哈希集合与哈希映射来跟踪并更新连续序列的长度。

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Longest Consecutive SequenceFeb 14

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.

public class Solution {
    public int longestConsecutive(int[] num) {
        // Start typing your Java solution below
        // DO NOT write main() function
        HashMap<Integer, Integer> ranges = new HashMap<Integer, Integer>();
        HashSet<Integer> unique = new HashSet<Integer>();
        int globeMax = 0;
        int sz = num.length;
        if(sz<1) return 0;
        for(int i=0; i<sz;i++) {
            int x = num[i];
            
            if( unique.contains(x) ) continue;
            else unique.add(x);
            
            int left = x;
            int right = x;
            
            
            if( ranges.containsKey(x-1) && ranges.get(x-1)<=x-1 ){
                left = ranges.get(x-1);
                ranges.remove(x-1);
            }
            
            if( ranges.containsKey(x+1) && ranges.get(x+1)>=x+1) {
                right = ranges.get(x+1);
                ranges.remove(x+1);
            }
            
            ranges.put(left, right);
            ranges.put(right,left);
            
            if( right-left+1>globeMax) globeMax = right-left+1;
        }
        
        return globeMax;
    }
}