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  • LeetCode——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.

    原题链接:https://oj.leetcode.com/problems/longest-consecutive-sequence/

    题目:给定一个未排序的整数数组,找出当中最长的递增元素序列的长度。

    你的算法的复杂度为O(N)。

    思路:使用HashSet,先将数组中的元素放入。去除了反复。同一时候,对数组中的每个元素。检測其左右側元素(+-1)是否在set集合中。

    	public static int longestConsecutive(int[] num) {
    		Set<Integer> set = new HashSet<Integer>();
    		int max = -1;
    		for (int ele : num)
    			set.add(ele);
    		for (int ele : num) {
    			int left = ele - 1;
    			int right = ele + 1;
    			int count = 1;
    			while (set.contains(left)) {
    				count++;
    				set.remove(left);
    				left--;
    			}
    			while (set.contains(right)) {
    				count++;
    				set.remove(right);
    				right++;
    			}
    			max = Math.max(count, max);
    		}
    		return max;
    	}


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  • 原文地址:https://www.cnblogs.com/yutingliuyl/p/6813132.html
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