HDU 2485 Destroying the bus stations (IDA*+ BFS)

傳送門：http://acm.hdu.edu.cn/showproblem.php?pid=2485

題意：給你n個點，m條相連的邊，問你最少去掉幾個點使從1到n最小路徑>=k，其中不能去掉1，n兩個點。

題解：這個題目可以用最小流解決，也可以用IDA*  +  BFS解決。

AC代碼：

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <cstdlib>#include <cmath>#include <vector>#include <list>#include <deque>#include <queue>#include <iterator>#include <stack>#include <map>#include <set>#include <algorithm>#include <cctype>using namespace std;#define si1(a) scanf("%d",&a)#define si2(a,b) scanf("%d%d",&a,&b)#define sd1(a) scanf("%lf",&a)#define sd2(a,b) scanf("%lf%lf",&a,&b)#define ss1(s)  scanf("%s",s)#define pi1(a)    printf("%d\n",a)#define pi2(a,b)  printf("%d %d\n",a,b)#define mset(a,b)   memset(a,b,sizeof(a))#define forb(i,a,b)   for(int i=a;i<b;i++)#define ford(i,a,b)   for(int i=a;i<=b;i++)typedef long long LL;const int N=1005;const int M=105;const int INF=0x3f3f3f3f;const double PI=acos(-1.0);const double eps=1e-7;int n,m,k;int lin[N][N];//鄰接表儲存int fa[N];//記錄從1到n最短路徑bool vis[N];//標記節點是否被刪除int ans,Min;bool flag;struct xh{    int x,y,next;}edge[N];int bfs(){    int q[2222];    int he=0,ta=0;    mset(fa,-1);    fa[1]=0;    mset(q,0);    q[ta++]=1;    while(he!=ta)    {        int x=q[he++];        for(int i=1;i<=lin[x][0];i++)        {            int v=lin[x][i];            if(fa[v]==-1&&!vis[v])            {                fa[v]=x;                q[ta++]=v;                if(n==v)    return 1;            }        }    }    return 0;}void dfs(int dian,int depth)//求去掉最少個數點{    if(flag==false) return ;    if(dian>depth) return ;    int p=bfs();    int sa[N]={0},t=0;    if(p==0){flag=false;return;}    for(int i=n;i!=1;i=fa[i])    {        sa[t++]=i;        if(t>k){flag=false;return ;}    }    for(int i=1;i<t;i++)    {        int x=sa[i];        if(vis[x])  continue;        vis[x]=1;        dfs(dian+1,depth);        vis[x]=0;        if(flag==false) return ;    }}void IDA(){    if(n<=2)    {        puts("0");        return ;    }    int depth=0;    flag=true;    vis[1]=1;    while(flag)    {        dfs(0,depth);        if(!flag)   break;        depth++;    }    pi1(depth);}int main(){//    freopen("input.txt","r",stdin);    while(scanf("%d%d%d",&n,&m,&k)&&(n+m+k))    {        mset(lin,0);        forb(i,0,m)        {            int a,b,t;            si2(a,b);            t=++lin[a][0];            lin[a][t]=b;            //這個地方寫雙向的就WA了，單向的就A了        }        IDA();    }    return 0;}

逾時代碼：（IDA*  +  DFS）個人感覺應該差不多，但是就是逾時了

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <cstdlib>#include <cmath>#include <vector>#include <list>#include <deque>#include <queue>#include <iterator>#include <stack>#include <map>#include <set>#include <algorithm>#include <cctype>using namespace std;#define si1(a) scanf("%d",&a)#define si2(a,b) scanf("%d%d",&a,&b)#define sd1(a) scanf("%lf",&a)#define sd2(a,b) scanf("%lf%lf",&a,&b)#define ss1(s)  scanf("%s",s)#define pi1(a)    printf("%d\n",a)#define pi2(a,b)  printf("%d %d\n",a,b)#define mset(a,b)   memset(a,b,sizeof(a))#define forb(i,a,b)   for(int i=a;i<b;i++)#define ford(i,a,b)   for(int i=a;i<=b;i++)typedef long long LL;const int N=1005;const int M=105;const int INF=0x3f3f3f3f;const double PI=acos(-1.0);const double eps=1e-7;int n,m,k;int lin[N][N];//鄰接表儲存int cnt[M];//記錄從1到n最短路徑bool vis[N];//標記節點是否被刪除int ans,Min;bool flag;struct xh{    int x,y,next;}edge[N];void dfs2(int k,int de)//求最短距離{    cnt[de]=k;//路徑    if(k==n)    {        Min=min(Min,de);        return ;    }    for(int i=1;i<=lin[k][0];i++)    {        int t=lin[k][i];        if(vis[t])  continue;        vis[t]=1;        dfs2(t,de+1);        vis[t]=0;    }}void dfs1(int dian,int depth)//求去掉最少個數點{    if(flag==false) return ;    Min=INF;    mset(cnt,0);    dfs2(1,0);//    cout<<"最短距離"<<Min<<endl;//    cout<<"路徑：";//    if(Min!=INF)//    {//        for(int i=0;i<=Min;i++)//            printf("%d ",cnt[i]);//        cout<<endl;//    }//    system("pause");    int xh=Min;    if(xh>=k)    {        flag=false;        ans=min(ans,dian);        return ;    }    if(dian>=depth)        return ;    int sa[N];    for(int i=0;i<=xh;i++)        sa[i]=cnt[i];    for(int i=1;i<xh;i++)    {        int t=sa[i];        if(vis[t])  continue;        vis[t]=1;        dfs1(dian+1,depth);        vis[t]=0;        if(flag==false) return ;    }}int main(){//    freopen("input.txt","r",stdin);    while(scanf("%d%d%d",&n,&m,&k)&&(n+m+k))    {        mset(lin,0);        forb(i,0,m)        {            int a,b,t;            si2(a,b);            t=++lin[a][0];            lin[a][t]=b;            t=++lin[b][0];            lin[b][t]=a;        }        ans=INF;        mset(vis,0);        vis[1]=1;        flag=true;        int depth=-1;        while(flag)        {            depth++;            dfs1(0,depth);        }        pi1(depth);    }    return 0;}