[Leetcode] 128. Longest Consecutive Sequence 解题报告
来源:互联网 发布:阿里云大数据平台 sql 编辑:程序博客网 时间:2024/05/29 16:13
题目:
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.
思路:
这道题目想清楚了就不难,但是想不清楚的话确实还不太好解决。标准的思路是:首先将数组中的所有元素都放在一个哈希表中(这是因为哈希表插入、删除以及查找的时间复杂度都可以近似地认为是O(1)),然后对数组中的元素进行扫描。对于每个被扫描到的元素,顺序查看和它相邻的数是否存在,如果存在,则长度加一,并且从哈希表中删除。这样当扫描完成整个数组之后,就得到了正确结果。本算法的空间复杂度是O(n),比较好理解。那么时间复杂度为什么也是O(n)呢?注意在第二个循环内部,虽然存在两个while循环,但是哈希表中的每个元素在for循环的过程中刚好仅被删除一次,所以总共而言,while循环内部的执行总次数也就是数组元素个数,所以总的时间复杂度也是O(n)。
代码:
class Solution {public: int longestConsecutive(vector<int>& nums) { unordered_set<int> hash; for(int i = 0; i < nums.size(); ++i) { hash.insert(nums[i]); } int max_length = 0; for(int i = 0; i < nums.size(); ++i) { if(hash.count(nums[i]) == 0) { continue; } int num = 0; int val = nums[i]; while(hash.count(val) > 0) { num++; hash.erase(val--); } val = nums[i] + 1; while(hash.count(val) > 0) { num++; hash.erase(val++); } max_length = max(max_length, num); } return max_length; }};
0 0
- [leetcode] 128. Longest Consecutive Sequence 解题报告
- [Leetcode] 128. Longest Consecutive Sequence 解题报告
- [LeetCode]Longest Consecutive Sequence, 解题报告
- 【LeetCode】Longest Consecutive Sequence 解题报告
- Leetcode 128. Longest Consecutive Sequence 最长连续序列 解题报告
- [leetcode] 298. Binary Tree Longest Consecutive Sequence 解题报告
- [Leetcode] 298. Binary Tree Longest Consecutive Sequence 解题报告
- [Leetcode] 549. Binary Tree Longest Consecutive Sequence II 解题报告
- 【LeetCode】Longest Consecutive Sequence解题笔记
- [LeetCode]128.Longest Consecutive Sequence
- [Leetcode] 128. Longest Consecutive Sequence
- [leetcode] 128.Longest Consecutive Sequence
- [leetcode] 128.Longest Consecutive Sequence
- Leetcode 128. Longest Consecutive Sequence
- Leetcode 128. Longest Consecutive Sequence
- LeetCode 128. Longest Consecutive Sequence
- LeetCode 128. Longest Consecutive Sequence
- [LeetCode]128. Longest Consecutive Sequence
- 第六 文本处理工具
- POJ 1128 Frame Stacking(拓扑排序)
- Crash符号化
- 分布式系统唯一ID生成方案
- 游戏图像学习入门到精通-Shader总结篇
- [Leetcode] 128. Longest Consecutive Sequence 解题报告
- c++之continue
- phpcms不允许评论仍然能提交评论的BUG修复
- 从tomcat迁移到websphere的问题记录
- 欢迎使用CSDN-markdown编辑器
- fedora20 dvd U盘安装
- Win 8 Python3 安装过程中遇到 KB2999226 卡住不动 或者弹出错误0x80240017 可以换成Python2.7来装
- C语言基础知识之四
- IOS--UITabBarController简单介绍