[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.

使用容器实现。已经判断过的不用再次判断。

 1 class Solution {

 2 public:

 3     int longestConsecutive(vector<int> &num) {

 4         map<int, int> mp;

 5         for (int i = 0; i < num.size(); ++i) {

 6             mp[num[i]] = 1;

 7         }

 8         int len = 0, tmp;

 9         for (int i = 0; i < num.size(); ++i) {

10             tmp = 1;

11             if (mp[num[i]] == 1) {

12                 int left = num[i] - 1;

13                 while (mp.count(left) && mp[left] == 1) {

14                     mp[left--] = 0;

15                     ++tmp;

16                 }

17                 int right = num[i] + 1;

18                 while (mp.count(right) && mp[right] == 1) {

19                     mp[right++] = 0;

20                     ++tmp;

21                 }

22                 len = (len > tmp) ? len : tmp;

23             }

24         }

25         return len;

26     }

27 };