HDU - 5001 Walk（概率dp+记忆化搜索）

标签：1.0   概率dp   col   vector   nta   node   sample   name   pre   

Walk

InputThe first line contains an integer T, denoting the number of the test cases. 

For each test case, the first line contains 3 integers n, m and d, denoting the number of vertices, the number of edges and the number of steps respectively. Then m lines follows, each containing two integers a and b, denoting there is an edge between node a and node b. 

T<=20, n<=50, n-1<=m<=n*(n-1)/2, 1<=d<=10000. There is no self-loops or multiple edges in the graph, and the graph is connected. The nodes are indexed from 1.OutputFor each test cases, output n lines, the i-th line containing the desired probability for the i-th node. 

Your answer will be accepted if its absolute error doesn‘t exceed 1e-5.Sample Input

2
5 10 100
1 2
2 3
3 4
4 5
1 5
2 4
3 5
2 5
1 4
1 3
10 10 10
1 2
2 3
3 4
4 5
5 6
6 7
7 8
8 9
9 10
4 9

Sample Output

0.0000000000
0.0000000000
0.0000000000
0.0000000000
0.0000000000
0.6993317967
0.5864284952
0.4440860821
0.2275896991
0.4294074591
0.4851048742
0.4896018842
0.4525044250
0.3406567483
0.6421630037




第一道比赛出的概率dp。找好状态记忆化搜索即可。

#include<bits/stdc++.h>
#define MAX 55
using namespace std;
typedef long long ll;

int n,m,k;
double ans;
double dp[MAX][10005];
vector<int> v[MAX];
double dfs(int f,int x,int s){
    int i;
    if(s>=k) return 1;
    if(dp[x][s]>-1) return dp[x][s];
    int xx=v[x].size();
    double cnt=0;
    for(i=0;i<v[x].size();i++){
        if(v[x][i]==f) continue;
        cnt+=dfs(f,v[x][i],s+1)*(1.0/xx);
    }
    dp[x][s]=cnt;
    return cnt;
}
int main()
{
    int t,i,j;
    int x,y;
    scanf("%d",&t);
    while(t--){
        scanf("%d%d%d",&n,&m,&k);
        for(i=1;i<=n;i++){
            v[i].clear();
        }
        for(i=1;i<=m;i++){
            scanf("%d%d",&x,&y);
            v[x].push_back(y);
            v[y].push_back(x);
        }
        for(i=1;i<=n;i++){
            ans=0;
            memset(dp,-1,sizeof(dp));
            for(j=1;j<=n;j++){
                if(i==j) continue;
                ans+=dfs(i,j,0)*(1.0/n);
            }
            printf("%.10f\n",ans);
        }
    }
    return 0;
}

HDU - 5001 Walk（概率dp+记忆化搜索）

标签：1.0   概率dp   col   vector   nta   node   sample   name   pre   

原文地址：https://www.cnblogs.com/yzm10/p/9665311.html