longest-consecutive-sequence.cc

// Longest Consecutive Sequence
class Solution {
public:
  int longestConsecutive(vector<int> &num) {
    int r = 0;
    unordered_set<int> s;
    for (auto i: num)
      s.insert(i);
    for (auto i: num) {
      int j = i, k = i+1;
      while (s.count(j-1)) s.erase(j--);
      while (s.count(k)) s.erase(k++);
      r = max(r, k-j);
    }
    return r;
  }
};