Codeforces Round #105 (Div. 2) D

搜索dp~注意 w 和 b 的值要大于0 ~否则会越界~

#include<iostream>#include<iomanip>#include<cstring>#include<cstdlib>#include<string>#include<vector>#include<algorithm>using namespace std;const int maxn=1024;const double eps = 1e-13;double dp[maxn][maxn];bool vis[maxn][maxn];double d2[maxn][maxn];bool v2[maxn][maxn];int ww,bb;double dwin(int w,int b);double pwin (int w,int b){    if(vis[w][b])    {        return dp[w][b];    }    double wx=w;    double bx=b;    double temp = 0.0;    temp +=  wx / (wx + bx);    temp +=  ( bx / ( wx + bx ) ) * ( 1.0 - dwin( w , b - 1 ) );    vis[w][b] = true;    dp[w][b] = temp;    return dp[w][b];}double dwin (int w,int b){    if(v2[w][b])    {        return d2[w][b];    }    double temp = 0.0;    double tw=0.0;    double tb=0.0;    double wx=w;    double bx=b;    temp += wx / (wx+bx);    if(w-1>=0 && b-1>=0)    {        tw = ( wx / ( wx + bx - 1.0 ) ) * ( 1.0 - pwin ( w - 1 , b - 1) );    }    if(b-2>=0)    {        tb = ( ( bx - 1.0 ) / ( wx + bx - 1.0 ) ) * ( 1.0 - pwin ( w , b - 2 ) );    }    temp += ( bx / ( wx + bx ) ) * (tw + tb);    v2[w][b] = true;    d2[w][b] = temp;    return d2[w][b];}int main(){    memset(vis,false,sizeof(vis));    memset(v2,false,sizeof(v2));    for(int i=1;i<maxn;i++)    {        vis[i][0] = true;        dp[i][0] = 1.0;        vis[0][i] = true;        dp[0][i] = 0.0;        v2[i][0] = true;        d2[i][0] = 1.0;        v2[0][i] = true;        d2[0][i] = 1.0;    }    v2[0][0]=vis[0][0]=true;    dp[0][0]=0.0;    d2[0][0]=1.0;    cout.setf(ios::fixed);    while(cin>>ww>>bb)    {        cout<<setprecision(9)<<pwin(ww,bb)<<endl;    }    return 0;}