leetcode - Longest Consecutive Sequence

题目描述：点击此处

这道题还是排序了，没能在O(n)的时间内解决，想了一个基于模的方法好久还没出结果，看网上都是用哈希表做得，个人不认同哈希表的访问时间为O(1)。

class Solution {
public:
  int longestConsecutive(vector<int> &num) {
    // Start typing your C/C++ solution below
    // DO NOT write int main() function
    if (num.size()<=0)
      return 0;
    sort(num.begin(),num.end());
    int len = 1;
    int max = 1;
    int last = *(num.begin());
    for (vector<int>::iterator ii= num.begin()+1; ii != num.end(); ii++){
      if (*ii == last)
        continue;
      else if (*ii== last +1){
        len ++;
        max = max >= len? max:len;
        last++;
      }
      else {
        last= *ii;
        len = 1;
      }
    }
    return max;
  }
};