128. Longest Consecutive Sequence

 1 class Solution {
 2 public:
 3     int longestConsecutive(vector<int>& nums) {
 4         if (nums.size() <= 1) return nums.size();
 5         else {
 6             map<int, int> used;
 7             for (const auto& item : nums) used[item] = 0;
 8             int count = 0, len = 0;
 9             for (size_t i = 0; i < nums.size(); ++i) {
10                 if (used[nums[i]] == 1) continue;
11                 count = 1;
12                 for (int j = nums[i] + 1; ; ++j) {
13                     if (used.find(j) != used.end() && used[j] == 0) {
14                         ++count; used[j] = 1;
15                     }
16                     else break;
17                 }
18                 for (int j = nums[i] - 1; ; --j) {
19                     if (used.find(j) != used.end() && used[j] == 0) {
20                         ++count; used[j] = 1;
21                     }
22                     else break;
23                 }
24                 if (count > len) len = count;
25             }
26             return len;
27         }
28     }
29 };