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.
用set保存所有元素，遍历数组中的每个元素，在set中查询是否有当前元素的左边元素和右边元素。
代码如下：
public int longestConsecutive(int[] nums) { if(nums == null) return 0; if(nums.length < 2) return nums.length; Set<Integer> set = new HashSet<Integer>(); for(int curr : nums) set.add(curr); int max = 1;//连续的最长长度 for(int curr:nums) { int left = curr-1; int right = curr+1; int count = 1; while(set.contains(left)) { set.remove(left); count++; left--; } while(set.contains(right)) { set.remove(right); count++; right++; } max = max > count ? max : count; } return max; }
LeetCode-Longest Consecutive Sequence
原文：http://www.cnblogs.com/linxiong/p/4498996.html