hdu 2485 Destroying the bus stations 迭代加深搜索

#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
#define maxn 60
#define maxm 50000
int n,m,K,cnt,up;
int head[maxn],pre[maxn];
int road[maxn][maxn];
bool del[maxn];
queue<int> Q;
bool flag;
struct Edge
{
    int from,to,next;
}e[maxm];
void make(int from,int to)
{
    e[cnt].from=from;
    e[cnt].to=to;
    e[cnt].next=head[from];
    head[from]=cnt++;
}
void bfs()
{
    int i;
    memset(pre,0,sizeof(pre));
    pre[1]=-1;
    Q.push(1);
    while(!Q.empty())
    {
        int u=Q.front();Q.pop();
        for(i=head[u];i!=-1;i=e[i].next)
        {
            if(del[e[i].to]==0&&pre[e[i].to]==0)
            {
                pre[e[i].to]=u;
                Q.push(e[i].to);
            }
        }
    }
}
void dfs(int x)
{
    int i;
    //if(flag==true) return ;
    bfs();
    if(pre[n]==0)
    {
        flag=true;
        return ;
    }
    int num=0;
    for(i=n;i!=-1;i=pre[i])
    {
        num++;
        road[x][num]=i;
    }
    for(i=1;i<=num;i++)
    if(num-1>K)
    {
        flag=true;
        return;
    }
    if(x>up) return;
    for(i=num-1;i>1;i--)
    {
        del[road[x][i]]=1;
        dfs(x+1);
        del[road[x][i]]=0;
    }

}
int main()
{
    while(1)
    {
        int i,j,u,v;
        scanf("%d%d%d",&n,&m,&K);
        if(n==0) break;
        cnt=0;
        flag=0;
        memset(head,-1,sizeof(head));
        for(i=1;i<=m;i++)
        {
            scanf("%d%d",&u,&v);
            make(u,v);
        }
        for(i=0;i<=n-2;i++)
        {
            up=i;
            memset(del,0,sizeof(del));
            dfs(1);
            if(flag==true)
                break;
        }
        printf("%d\n",up);
    }
    return 0;
}