题目描述:(链接)
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.
解题思路:
题目要求时间复杂度O(n),于是想到了哈希表,记录每个元素的使用情况,求出最长的长度。
class Solution { public: int longestConsecutive(vector<int>& nums) { unordered_map<int, bool> used; int longest = 0; for (auto i : nums) { used[i] = false; } for (auto i : nums) { if (used[i]) { continue; } int length = 1; for (int j = i + 1; used.find(j) != used.end(); ++j) { used[j] = true; ++length; } for (int j = i - 1; used.find(j) != used.end(); --j) { used[j] = true; ++length; } if (length > longest) { longest = length; } } return longest; } };