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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.
复杂度要求o(n)，用哈希或者构建辅助数组
把元素存入哈希
遍历数组，找每个元素能够引出的序列长度
class Solution { public: int longestConsecutive(vector<int>& nums) { int numsSize = nums.size(); unordered_map<int,bool> allNums; int res = 0; for(int i=0;i<numsSize;i++){ allNums[nums[i]]=true; } for(int i=0;i<numsSize;i++){ int cur = nums[i]; if(!allNums[cur]){ continue; } int cnt = 1; int pre = cur-1; while(allNums[pre]){ cnt++; allNums[pre] = false; pre--; } int next = cur+1; while(allNums[next]){ cnt++; allNums[next] = false; next++; } allNums[cur] = false; res = max(res,cnt); } return res; } };
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原文地址：http://www.cnblogs.com/zengzy/p/5004437.html
