A11705 | Circles of Waiting
时间限制1s
内存限制256MB
通过 / 提交0/0
题目描述
A chip was placed on a field with coordinate system onto point $(0,0)$ .
Every second the chip moves randomly. If the chip is currently at a point $(x,y)$ , after a second it moves to the point $(x-1,y)$ with probability $p_{1}$ , to the point $(x,y-1)$ with probability $p_{2}$ , to the point $(x+1,y)$ with probability $p_{3}$ and to the point $(x,y+1)$ with probability $p_{4}$ . It's guaranteed that $p_{1}+p_{2}+p_{3}+p_{4}=1$ . The moves are independent.
Find out the expected time after which chip will move away from origin at a distance greater than $R$ (i.e.  will be satisfied).
Every second the chip moves randomly. If the chip is currently at a point $(x,y)$ , after a second it moves to the point $(x-1,y)$ with probability $p_{1}$ , to the point $(x,y-1)$ with probability $p_{2}$ , to the point $(x+1,y)$ with probability $p_{3}$ and to the point $(x,y+1)$ with probability $p_{4}$ . It's guaranteed that $p_{1}+p_{2}+p_{3}+p_{4}=1$ . The moves are independent.
Find out the expected time after which chip will move away from origin at a distance greater than $R$ (i.e.  will be satisfied).
输入格式
First line contains five integers $R,a_{1},a_{2},a_{3}$ and $a_{4}$ ( $0<=R<=50,1<=a_{1},a_{2},a_{3},a_{4}<=1000$ ).
Probabilities $p_{i}$ can be calculated using formula .
Probabilities $p_{i}$ can be calculated using formula .
输出格式
It can be shown that answer for this problem is always a rational number of form , where .
Print $P·Q^{-1}$ modulo $10^{9}+7$ .
Print $P·Q^{-1}$ modulo $10^{9}+7$ .
输入输出样例
输入 #1
0 1 1 1 1
输出 #1
1
输入 #2
1 1 1 1 1
输出 #2
666666674
输入 #3
1 1 2 1 2
输出 #3
538461545
In the first example initially the chip is located at a distance $0$ from origin. In one second chip will move to distance $1$ is some direction, so distance to origin will become $1$ .
Answers to the second and the third tests:  and .
Answers to the second and the third tests:  and .
C++ 编辑器
输入
输出
可保存默认模板;新题优先使用已保存模板。
当前快捷键仅展示,暂不支持修改。
- 撤销
Ctrl / ⌘ + Z - 重做
Ctrl / ⌘ + Y - 查找
Ctrl / ⌘ + F - 全选
Ctrl / ⌘ + A - 复制
Ctrl / ⌘ + C - 剪切
Ctrl / ⌘ + X - 粘贴
Ctrl / ⌘ + V - 自动排版
工具栏排版按钮 - 草稿保存
编辑时自动保存到本机
历史
提交记录
状态说明时间源码
AI
作答助手
你好,我是作答助手。可以问思路、复杂度、样例含义或代码报错原因;不会直接给出完整 AC 代码。
确定要清空代码吗?
提交通过
评测结果:Accepted