【LeetCode】785. Is Graph Bipartite? 解题报告(Python)

作者: 负雪明烛
id: fuxuemingzhu
个人博客: http://fuxuemingzhu.cn/


题目地址:https://leetcode.com/problems/is-graph-bipartite/description/

题目描述:

Given an undirected graph, return true if and only if it is bipartite.

Recall that a graph is bipartite if we can split it’s set of nodes into two independent subsets A and B such that every edge in the graph has one node in A and another node in B.

The graph is given in the following form: graph[i] is a list of indexes j for which the edge between nodes i and j exists. Each node is an integer between 0 and graph.length - 1. There are no self edges or parallel edges: graph[i] does not contain i, and it doesn’t contain any element twice.

Example 1:

Input: [[1,3], [0,2], [1,3], [0,2]]
Output: true
Explanation:
The graph looks like this:
0----1
| |
| |
3----2
We can divide the vertices into two groups: {0, 2} and {1, 3}.

Example 2:

Input: [[1,2,3], [0,2], [0,1,3], [0,2]]
Output: false
Explanation:
The graph looks like this:
0----1
| \ |
| \ |
3----2
We cannot find a way to divide the set of nodes into two independent subsets.

Note:

  1. graph will have length in range [1, 100].
  2. graph[i] will contain integers in range [0, graph.length - 1].
  3. graph[i] will not contain i or duplicate values.
  4. The graph is undirected: if any element j is in graph[i], then i will be in graph[j].

题目大意

判断一个无向图是不是二分图。二分图的定义是,可以把一个图划分成两部分,使得图中的每个边的两个定点分别来自这两部分。

解题方法

这个题很容易理解了,做法也很简单,使用众所周知的染色法。可以通过BFS或者DFS来解决。我使用的是BFS.

使用一个visited数组来保存每个节点被染的颜色。0代表没染色,1代表染成蓝色,2代表染成红色。对图的每个顶点进行一个遍历,把和这个顶点相邻的顶点全部染成相反的颜色。如果相邻顶点已经染色,而且染色和当前顶点染色相同,则返回False。全部成功染色后返回True。

这个题没有说明是连通图,这个就很坑爹了,不能通过一次的BFS就把所有的顶点染色成功。所以需要的是一个外层的对顶点进行遍历,一个内层的对每个顶点相邻的顶点遍历,这样两重遍历才能保证每个顶点、这个顶点相邻的顶点都被强行的染色。

时间复杂度是O(E+V),空间复杂度是O(E).

代码如下:

class Solution(object):
def isBipartite(self, graph):
"""
:type graph: List[List[int]]
:rtype: bool
"""
visited = [0] * len(graph)# 0-not visited; 1-blue; 2-red;
for i in range(len(graph)):
if graph[i] and visited[i] == 0:
visited[i] = 1
q = collections.deque()
q.append(i)
while q:
v = q.popleft()#every point
for e in graph[v]:#every edge
if visited[e] != 0:
if visited[e] == visited[v]:
return False
else:
visited[e] = 3 - visited[v]
q.append(e)
return True

参考资料:

https://leetcode.com/problems/is-graph-bipartite/discuss/115503/java-BFS

日期

2018 年 9 月 20 日 —— 趁年轻多读书

【LeetCode】785. Is Graph Bipartite? 解题报告(Python)的更多相关文章

  1. [leetcode]785. Is Graph Bipartite? [bai'pɑrtait] 判断二分图

    Given an undirected graph, return true if and only if it is bipartite. Example 1: Input: [[1,3], [0, ...

  2. [LeetCode] 785. Is Graph Bipartite? 是二分图么?

    Given an undirected graph, return true if and only if it is bipartite. Recall that a graph is bipart ...

  3. LeetCode 785. Is Graph Bipartite?

    原题链接在这里:https://leetcode.com/problems/is-graph-bipartite/ 题目: Given an undirected graph, return true ...

  4. [LeetCode] 785. Is Graph Bipartite?_Medium tag: DFS, BFS

    Given an undirected graph, return true if and only if it is bipartite. Recall that a graph is bipart ...

  5. 【LeetCode】62. Unique Paths 解题报告(Python & C++)

    作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 题目地址:https://leetcode.com/problems/unique-pa ...

  6. 【LeetCode】886. Possible Bipartition 解题报告(Python)

    [LeetCode]886. Possible Bipartition 解题报告(Python) 作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu ...

  7. 【LeetCode】376. Wiggle Subsequence 解题报告(Python)

    [LeetCode]376. Wiggle Subsequence 解题报告(Python) 作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.c ...

  8. 【LeetCode】649. Dota2 Senate 解题报告(Python)

    [LeetCode]649. Dota2 Senate 解题报告(Python) 作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 题目地 ...

  9. 【LeetCode】911. Online Election 解题报告(Python)

    [LeetCode]911. Online Election 解题报告(Python) 作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ ...

随机推荐

  1. liveBOS环境搭建

    环境搭建:1.准备jdk1.6及以上版本oracle11gplsqlsql脚本(oracle_init.sql,oracle_insert.sql)livebos_tomcatlivebos的授权文件 ...

  2. Vector总结及部分底层源码分析

    Vector总结及部分底层源码分析 1. Vector继承的抽象类和实现的接口 Vector类实现的接口 List接口:里面定义了List集合的基本接口,Vector进行了实现 RandomAcces ...

  3. python-3.x- 序列操作

    1. list操作 A.添加元素 1 list = ["C++","C", "Java", "Python"] 2 &q ...

  4. hadoop运行jar包报错

    执行命令:[root@hadoop102 mapreduce]# hadoop jar mapreduce2_maven.jar Filter 错误信息:Exception in thread &qu ...

  5. A Child's History of England.48

    A few could not resolve to do this, but the greater part complied. They made a blazing heap of all t ...

  6. Spark(四)【RDD编程算子】

    目录 测试准备 一.Value类型转换算子 map(func) mapPartitions(func) mapPartitions和map的区别 mapPartitionsWithIndex(func ...

  7. OC简单介绍

    一.OC与C的对比 关键字 OC新增的关键字在使用时,注意部分关键字以"@"开头 方法->函数 定义与实现 数据类型 新增:BOOL/NSObject/id/SEL/bloc ...

  8. KVM配置

    安装依赖包(因最小化安装) [root@slave-master ~]# yum install -y vim wget tree lrzsz gcc gcc-c++ automake pcre pc ...

  9. 【Linux】【Shell】【Basic】函数

    1. 函数:function,把一段独立功能的代码当作一个整体,并为之一个名字:命名的代码段,此即为函数: 注意:定义函数的代码段不会自动执行,在调用时执行:所谓调用函数,在代码中给定函数名即可: 函 ...

  10. 【Python】数据处理分析,一些问题记录

    不用造轮子是真的好用啊 python中单引号双引号的区别 和cpp不一样,cpp单引号表示字符,双引号表示字符串,'c'就直接是ascii值了 Python中单引号和双引号都可以用来表示一个字符串 单 ...