HDU 4751 Divide Groups（判断是否为二分图)

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#define LL long long
#define FOR(i, x, y) for(int i=x;i<=y;i++)
using namespace std;
const int MAXN = 100 + 10;
struct Edge
{
int to;
int next;
}edge[MAXN*MAXN];
int head[MAXN];
int G[MAXN][MAXN];
int col[MAXN];
int tot;
void AddEdge(int u, int v)
{
edge[tot].to = v;
edge[tot].next = head[u];
head[u] = tot++;
}
void init()
{
tot = 0;
memset(head, -1, sizeof(head));
}
bool dfs(int u, int c)
{
col[u] = c;
for(int i=head[u];i!=-1;i=edge[i].next)
{
int v = edge[i].to;
if(col[v] != -1)
{
if(col[v] == c)
return false;
}
else if(!dfs(v, col[u]^1))
return false;
}
return true;
}
int main()
{
int n;
while(scanf("%d", &n)!=EOF && n)
{
memset(G, 0, sizeof(G));
int t;
FOR(i, 1, n)
{
while(scanf("%d", &t) && t)
{
G[i][t] = 1;
}
}
init();
FOR(i, 1, n)
{
FOR(j, i + 1, n)
{
if(G[i][j] == 0 || G[j][i] == 0)
{
AddEdge(i, j);
AddEdge(j, i);
}
}
}
memset(col, -1, sizeof(col));
int flag = 1;
for(int i=1;i<=n;i++)
{
if(col[i] == -1 && dfs(i, 0) == false)
{
flag = 0;
break;
}
}
if(flag) printf("YES\n");
else printf("NO\n");
}
return 0;
}