HDU 1693 Eat the Trees

插头DP，多条回路求回路数。

可以当作模版来记。注重理解轮廓线。

#include <iostream>#include <string.h>#include <iostream>#include <stdio.h>using namespace std;const int HASH=10007;const int STATE=5000; //状态数const int MAXD=15;int code[MAXD],maze[MAXD][MAXD];int N,M;struct HASHMAP{int head[HASH],next[STATE],state[STATE],size;long long f[STATE];void init(){size=0;memset(head,-1,sizeof(head));}void push(int st,long long ans){int i,h=st%HASH;for(i=head[h];i!=-1;i=next[i])if(st==state[i]){f[i]+=ans;return;}f[size]=ans;state[size]=st;next[size]=head[h];head[h]=size++;}}hm[2];void decode(int *code,int m,int st){int i;for(i=m;i>=0;i--){code[i]=st&1;st>>=1;}}int encode(int *code,int m){int i,st=0;for(i=0;i<=m;i++){st<<=1;st|=code[i];}return st;}void init(){scanf("%d%d",&N,&M);for(int i=1;i<=N;i++)for(int j=1;j<=M;j++)scanf("%d",&maze[i][j]);for(int i=1;i<=N;i++)maze[i][M+1]=0;for(int i=1;i<=M;i++)maze[N+1][i]=0;//边界补0}void shift(int *code,int m)//换行{int i;for(i=m;i>0;i--)code[i]=code[i-1];code[0]=0;}void dpblank(int i,int j,int cur){int k,left,up;for(k=0;k<hm[cur].size;k++){decode(code,M,hm[cur].state[k]);left=code[j-1];up=code[j];if(left&&up)//左边和上边都有插头{code[j-1]=code[j]=0;if(j==M)shift(code,M);hm[cur^1].push(encode(code,M),hm[cur].f[k]);}else if(left||up){if(maze[i][j+1]){code[j-1]=0;code[j]=1;hm[cur^1].push(encode(code,M),hm[cur].f[k]);}if(maze[i+1][j]){code[j-1]=1;code[j]=0;if(j==M)shift(code,M);hm[cur^1].push(encode(code,M),hm[cur].f[k]);}}else{if(maze[i+1][j]&&maze[i][j+1]){code[j]=code[j-1]=1;hm[cur^1].push(encode(code,M),hm[cur].f[k]);}}}}void dpblock(int i,int j,int cur){int k;for(k=0;k<hm[cur].size;k++){decode(code,M,hm[cur].state[k]);code[j-1]=code[j]=0;if(j==M)shift(code,M);hm[cur^1].push(encode(code,M),hm[cur].f[k]);}}void solve(){int i,j,cur;long long ans=0;cur=0;hm[cur].init();hm[cur].push(0,1);for(i=1;i<=N;i++)for(j=1;j<=M;j++){hm[cur^1].init();if(maze[i][j])dpblank(i,j,cur);else dpblock(i,j,cur);cur^=1;}for(i=0;i<hm[cur].size;i++)ans+=hm[cur].f[i];printf("There are %I64d ways to eat the trees.\n",ans);}int main(){/*freopen("in.txt","r",stdin);freopen("out.txt","w",stdout);*/int T;int iCase=0;scanf("%d",&T);while(T--){iCase++;printf("Case %d: ",iCase);init();solve();}return 0;}