第四届 The number of steps

最新推荐文章于 2020-09-09 11:06:46 发布

转载最新推荐文章于 2020-09-09 11:06:46 发布 · 62 阅读

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原文链接：http://www.cnblogs.com/MisdomTianYa/p/6581749.html

本文探讨了一种特殊的三角形迷宫结构，每个房间只能前往左侧及下侧房间。从顶层出发寻找位于最底层左端的钥匙。通过概率分析，计算到达钥匙所需的期望步骤数。

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Description

Mary stands in a strange maze, the maze looks like a triangle（the first layer have one room，the second layer have two rooms，the third layer have three rooms …）. Now she stands at the top point(the first layer), and the KEY of this maze is in the lowest layer’s leftmost room. Known that each room can only access to its left room and lower left and lower right rooms .If a room doesn’t have its left room, the probability of going to the lower left room and lower right room are a and b (a + b = 1 ). If a room only has it’s left room, the probability of going to the room is 1. If a room has its lower left, lower right rooms and its left room, the probability of going to each room are c, d, e (c + d + e = 1). Now , Mary wants to know how many steps she needs to reach the KEY. Dear friend, can you tell Mary the expected number of steps required to reach the KEY?

Input

There are no more than 70 test cases.

In each case , first Input a positive integer n(0<n<45), which means the layer of the maze, then Input five real number a, b, c, d, e. (0<=a,b,c,d,e<=1, a+b=1, c+d+e=1).

The input is terminated with 0. This test case is not to be processed.

Output

Please calculate the expected number of steps required to reach the KEY room, there are 2 digits after the decimal point.

Sample Input

30.3 0.70.1 0.3 0.60

Sample Output

3.41

#include <iostream>
#include <cstdio>
#include <math.h>
#include <iomanip>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <string>
#include <queue>
using namespace std;

int main()
{
    int N;
    while(cin>>N&&N!=0)
    {
        double A[50][50]={0.0};
        double a,b,c,d,e;
        cin>>a>>b>>c>>d>>e;
        A[N][1]=0;
        for(int i=2;i<=N;i++)
            A[N][i]=A[N][i]+A[N][i-1]+1;
        for(int i=N-1;i>=1;i--)
            for(int j=1;j<=i;j++)
           {
              if(j==1)
                A[i][j]+=a*(A[i+1][j]+1)+b*(A[i+1][j+1]+1);
              else
                A[i][j]+=e*(A[i][j-1]+1)+d*(A[i+1][j+1]+1)+c*(A[i+1][j]+1);
           }
        cout<<setiosflags(ios::fixed)<<setprecision(2);
        cout<<A[1][1]<<endl;
    }
    return 0;
}

转载于:https://www.cnblogs.com/MisdomTianYa/p/6581749.html