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.

// https://oj.leetcode.com/problems/longest-consecutive-sequence/
// Author : Chao Zeng
// Date   : 2015-3-30
class Solution {
public:
    int longestConsecutive(vector
  
    &num) {
        map
   
     mp; const int NUM = 100;//由于数据中存在负数，所以数组元素加一个偏移量，保证数组下标有效性 int length = num.size(); for (int i = 0; i < length; i++){ mp[num[i] + NUM] = 1; } int ans; int res = 0; for (int i = 0; i < length; i++){ ans = 1; if (mp.count(num[i] + NUM)){ int left = num[i] + NUM - 1; while (mp.count(left) && mp[left] != 0){ mp[left--] = 0; ans++; } int right = num[i] + NUM + 1; while (mp.count(right) && mp[right] != 0){ mp[right++] = 0; ans++; } } if (res < ans){ res = ans; } } return res; } };
   
  

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