[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.

 

class Solution {
public:
      int longestConsecutive(const vector<int> &nums) {
        unordered_map<int, int> map;
        int result = 0;
        for (auto i: nums){
            if (map.find(i) = map.end()){
            int left = map.find(i - 1) != map.end() ? map[i - 1]: 0;
            int right = map.find(i + 1) != map.end() ? map[i + 1]: 0;
            int lenght = left + right + 1;
            map[i] = length;
            map[i - left] = length;
            map[i + right] = length;
            result = max(result, length);
            } 
        }
        return result; 
      }
};

　　

class Solution {
public:
      int longestConsecutive(const vector<int> &nums) {
        unordered_map<int, bool> map;
        for (auto i: nums) map[i] = false;
        int result = 0;
        for (auto i: nums){
            if (map[i]) continue;
            map[i] = true;
            int length = 1;
            for (int j = i + 1; map.find(j) != map.end(); j++){
                map[j] = true;
                length += 1;
            }

            for (int j = i - 1; map.find(j) != map.end(); j--){
                map[j] = true;
                length += 1;
            }
            result = max(result, length);
        }
        return result; 
      }
};