Question:
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:
1 class Solution { 2 public: 3 int longestConsecutive(vector<int>& num) { 4 map<int,bool> used; 5 for(vector<int>::const_iterator iter=num.begin();iter!=num.end();iter++) 6 { 7 used[*iter]=false; 8 } 9 int longest=0; 10 for(vector<int>::const_iterator ptr=num.begin();ptr!=num.end();ptr++) 11 { 12 if(used[*ptr]) 13 continue; 14 int max_length=1; 15 used[*ptr]=true; 16 for(int j=*ptr+1;used.find(j)!=used.end();j++) 17 { 18 used[j]=true; 19 max_length++; 20 } 21 for(int j=*ptr-1;used.find(j)!=used.end();j--) 22 { 23 used[j]=true; 24 max_length++; 25 } 26 longest=max(longest,max_length); 27 } 28 29 return longest; 30 } 31 };
原文：http://www.cnblogs.com/riden/p/4631444.html