hdu4751Divide Groups【判断二分图】

Total Submission(s): 1904    Accepted Submission(s): 676


[align=left]Problem Description[/align]



  This year is the 60th anniversary of NJUST, and to make the celebration more colorful, Tom200 is going to invite distinguished alumnus back to visit and take photos.

  After carefully planning, Tom200 announced his activity plan, one that contains two characters:

  1. Whether the effect of the event are good or bad has nothing to do with the number of people join in.

  2. The more people joining in one activity know each other, the more interesting the activity will be. Therefore, the best state is that, everyone knows each other.

  The event appeals to a great number of alumnus, and Tom200 finds that they may not know each other or may just unilaterally recognize others. To improve the activities effects, Tom200 has to divide all those who signed up into groups to take part in the activity
at different time. As we know, one's energy is limited, and Tom200 can hold activity twice. Tom200 already knows the relationship of each two person, but he cannot divide them because the number is too large.

  Now Tom200 turns to you for help. Given the information, can you tell if it is possible to complete the dividing mission to make the two activity in best state.

 

[align=left]Input[/align]
  The input contains several test cases, terminated by EOF.

  Each case starts with a positive integer n (2<=n<=100), which means the number of people joining in the event.

  N lines follow. The i-th line contains some integers which are the id

of students that the i-th student knows, terminated by 0. And the id starts from 1.
 

[align=left]Output[/align]
  If divided successfully, please output "YES" in a line, else output "NO".

 

[align=left]Sample Input[/align]

3
3 0
1 0
1 2 0

 

[align=left]Sample Output[/align]

YES

 

[align=left]Source[/align]
2013 ACM/ICPC Asia Regional Nanjing Online

 

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自己好菜啊QAQ 题意：给出彼此认识的关系（不传递），问是否可以分成两部分使得两部分中都互相认识

裸的判断二分图，模板手误写错了两个单词，最大的问题是最开始为标记数组赋值的时候是单向的！加边的时候是双向的==

再有，难道不应该染色的时候只在for循环外面只赋值一次吗？为什么写里面写外面都对啊==

#include <iostream>
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
int col[200],n,x;
vector<int>G[200];
bool flag[200][200];
bool dfs(int u,int color)
{
col[u]=color;
for(int i=0;i<G[u].size();i++)
{
int v=G[u][i];
if(col[v]==color) return false;
if(col[v]==-1)
{
if(!dfs(v,!color)) return false;
}
}
return true;
}
int main()
{
// freopen("cin.txt","r",stdin);
while(~scanf("%d",&n))
{
for(int i=1;i<=n;i++) G[i].clear();
memset(flag,0,sizeof(flag));
for(int i=1;i<=n;i++)
{
while(scanf("%d",&x)&&x)
{
flag[i][x]=1;
// flag[x][i]=1;
}
}
for(int i=1;i<=n;i++)
{
for(int j=1;j<=n;j++)
{
if(i==j) continue;
if(0==flag[i][j]||0==flag[j][i])
{
G[i].push_back(j);G[j].push_back(i);
}
}
}

bool fl=true;
memset(col,-1,sizeof(col));
for(int i=1;i<=n&&fl;i++)
{

if(col[i]==-1)
{
if(!dfs(i,0)) fl=false;
}
}
if(fl) puts("YES");
else puts("NO");
}
return 0;
}