hdu4751 Divide Groups

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.

 

Input

  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.

 

Output

  If divided successfully, please output "YES" in a
line, else output "NO".

 

Sample Input

3
3 0
1 0
1 2 0

 

Sample Output

YES

/*
二分图染色模板题
*/
#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#include<vector>
#define ll long long
using namespace std;
const int maxn = ;
int n,col[maxn];
bool kw[maxn][maxn];
vector<int> g[maxn];
bool dfs(int x,int c){
    col[x] = c;
    int to;
    for(int i = ;i < g[x].size();i++){
        to = g[x][i];
        if(col[to] == c) return false;
        if(!col[to] && !dfs(to,-c)) return false;
    }
    return true;
}
void get_ans(){
    for(int i = ;i <= n;i++){
        if(!col[i]){
            if(!dfs(i,)){
                printf("NO\n");
                return;
            }
        }
    }
    printf("YES\n");
}
int main(){
    int to;
    while(scanf("%d",&n) == ){
        for(int i = ;i <= n;i++) g[i].clear();
        memset(col,,sizeof(col));
        memset(kw,,sizeof(kw));
        for(int i = ;i <= n;i++){
            while(scanf("%d",&to) == &&to){
                kw[i][to] = true;
            }
        }
        for(int i = ;i <= n;i++){
            for(int j = i + ;j <= n;j++){
                if(!kw[i][j] || !kw[j][i]){
                    g[i].push_back(j);
                    g[j].push_back(i);
                }
            }
        }
        get_ans();
    }
    return ;
}