zoj 3822 Domination 概率dp

#include<iostream>#include<cstring>#include<cstdio>using namespace std;int T;int l,c;double dp[2605][55][55];bool b[2605][55][55];double DP(int k,int x,int y){    if(x>=l&&y>=c)return 0;    if(b[k][x][y])return dp[k][x][y];    if(x==0||y==0)return DP(k+1,x+1,y+1)+1;    int st = x*y-k;int lst = l*c-k;int las = (l-x)*(c-y);    double ans = 0;    //if(lst==0)return 0;    if(k<x*y)ans += DP(k+1,x,y)*(st/(1.0*lst));    if(x<l)ans+=(l-x)*y/(1.0*lst)*DP(k+1,x+1,y);    if(y<c)ans+=(c-y)*x/(1.0*lst)*DP(k+1,x,y+1);    if(x<l&&y<c)ans+=las/(1.0*lst)*DP(k+1,x+1,y+1);    b[k][x][y]=1;    return dp[k][x][y] = ans+1;}int main(){    scanf("%d",&T);    while(T--){        memset(dp,0,sizeof(dp));memset(b,0,sizeof(b));        scanf("%d%d",&l,&c);        printf("%.12lf\n",DP(0,0,0));    }}