hdu5794 A Simple Chess 容斥+Lucas 从(1,1)开始出发，每一步从(x1,y1)到达(x2,y2)满足(x2−x1)^2+(y2−y1)^2=5, x2>x1,y2>y1; 其实就是走日字。而且是往(n,m)方向走的日字。还有r个障碍物，障碍物不可以到达。求(1,1)到(n,m)的路径条数。

A Simple Chess

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 2597    Accepted Submission(s): 691

Problem Description

There is a n×m board, a chess want to go to the position
(n,m) from the position (1,1).
The chess is able to go to position (x2,y2) from the position (x1,y1), only and if only x1,y1,x2,y2 is satisfied that (x2−x1)2+(y2−y1)2=5, x2>x1, y2>y1.
Unfortunately, there are some obstacles on the board. And the chess never can stay on the grid where has a obstacle.
I want you to tell me, There are how may ways the chess can achieve its goal.

 

Input

The input consists of multiple test cases.
For each test case:
The first line is three integers, n,m,r,(1≤n,m≤1018,0≤r≤100), denoting the height of the board, the weight of the board, and the number of the obstacles on the board.
Then follow r lines, each lines have two integers, x,y(1≤x≤n,1≤y≤m), denoting the position of the obstacles. please note there aren't never a obstacles at position (1,1).

 

Output

For
each test case,output a single line "Case #x: y", where x is the case
number, starting from 1. And y is the answer after module 110119.

 

Sample Input

1 1 0
3 3 0
4 4 1
2 1
4 4 1
3 2
7 10 2
1 2
7 1

 

Sample Output

Case #1: 1
Case #2: 0
Case #3: 2
Case #4: 1
Case #5: 5

 

Author

UESTC

 

Source

2016 Multi-University Training Contest 6

 

 

/**
题目：A Simple Chess
链接：http://acm.hdu.edu.cn/showproblem.php?pid=5794
题意：从(1,1)开始出发，每一步从(x1,y1)到达(x2,y2)满足(x2−x1)^2+(y2−y1)^2=5, x2>x1,y2>y1;
其实就是走日字。而且是往(n,m)方向走的日字。还有r个障碍物，障碍物不可以到达。求(1,1)到(n,m)的路径条数。
思路：容斥+Lucas

如果没有障碍物：那么每一次可以选择从(x1,y1)到达(x1+2,y1+1)或者(x1+1,y1+2)；
那么设选择了x次(x1+2,y1+1),y次(x1+1,y1+2)
那么： x1+2*x+y = n;  => 2*x+y = n-x1;
       x+2*y+y1 = m;     2*y+x = m-y1;

x = (2*n-2*x1-m+y1)/3;
y = (2*m-2*y1-n+x1)/3;  说明如果2*n-2*x1-m+y1或者2*m-2*y1-n+x1不是3的倍数，（x,y都必须非负整数），那么无法到达。

否则路径条数为：C(x+y,x)；

存在障碍物：
假设只有一个障碍物，那么用总的路径条数sum-经过这一个障碍物的路径条数dp[1]。
假设存在两个障碍物，那么sum-经过的第一个障碍物为编号1的路径条数-经过的第一个障碍物为编号2的路径条数。（注意：第一个！！！）

经过的第一个障碍物为编号1的路径条数：从(1,1)到达(x1,y1)的路径条数乘以(x1,y1)到达(n,m)的路径条数。
经过的第一个障碍物为编号2的路径条数：（从(1,1)到达(x2,y2)的路径条数-从(1,1)到达(x1,y1)然后从(x1,y1)到达(x2,y2)的路径条数）
乘以 从(x2,y2)到达(n,m)的路径条数。

当多个障碍物时，方法同上处理。

处理c(x+y,x)%mod用Lucas定理。
*/

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<int,int> P;
const int maxn = 1e6+;
const int mod = ;
LL f[mod+];///阶乘。
LL inv[mod+];///逆元
LL exgcd(LL a, LL b, LL &x, LL &y)///扩展欧几里得；
{
    if (!b)
    {
        x = ;
        y = ;
        return a;
    }
    LL gcd = exgcd(b, a % b, x, y);
    LL t = x;
    x = y;
    y = t - (a / b) * x;
    return gcd;
}
LL inverse(LL num, LL mod)///求逆元；
{
    LL x, y;
    exgcd(num, mod, x, y);
    return (x % mod + mod) % mod;
}
void init()///如果mod小，那么可以线性筛逆元。
{
    inv[] = ;
    for(int i = ; i < mod; i++){
        inv[i] = (mod-mod/i)*inv[mod%i]%mod;
    }
    f[] = ;
    for(int i = ; i < mod; i++){///预处理阶乘。
        f[i] = f[i-]*i%mod;
    }
}
LL mult(LL a,LL b,LL p)///解决 大数a*b%p溢出long long 的方法；
{
    LL ans=;
    while(b)
    {
        if(b&)
            ans=(ans+a)%p;
        b>>=;
        a=(a+a)%p;
    }
    return ans;
}
LL C(LL a, LL b, LL mod)///实现C(n,m)%p
{

    if (b > a)
        return ;
    return mult(mult(f[a],inv[f[b]],mod),inv[f[a-b]],mod);/// a!/(b!*(a-b)!);
}
LL lucas(LL n, LL m, LL p)///卢卡斯定理实现；c(n,m)%p；
{
    if (m == )
        return ;
    return mult(C(n % p, m % p, p),lucas(n / p, m / p, p),p);
}
LL solve(LL x1,LL y1,LL n,LL m)
{
    if((*n-*x1-m+y1)%!=) return ;
    if((*m-*y1-n+x1)%!=) return ;
    LL x = (*n-*x1-m+y1)/;
    LL y = (*m-*y1-n+x1)/;
    if(x<||y<) return ;
    return lucas(x+y,y,mod)%mod;
}
LL n, m, r;
struct node
{
    LL x, y;
    bool operator < (const node&k)const{
        if(x==k.x) return y<k.y;
        return x<k.x;
    }
}t[];
LL ans[];
int main()
{
    int cas = ;
    init();///初始化逆元。
    while(scanf("%lld%lld%lld",&n,&m,&r)!=EOF)
    {
        for(int i = ; i < r; i++){
            scanf("%lld%lld",&t[i].x,&t[i].y);
        }
        sort(t,t+r);

        LL sum = solve(,,n,m);
        for(int i = ; i < r; i++){
            ans[i] = solve(,,t[i].x,t[i].y);
            for(int j = ; j < i; j++){
                ans[i] = (ans[i]-ans[j]*solve(t[j].x,t[j].y,t[i].x,t[i].y)%mod+mod)%mod;
            }
        }
        //cout<<"sum = "<<sum<<endl;
        //cout<<"ans[0] = "<<ans[0]<<endl;
        for(int i = ; i < r; i++){
            sum = (sum-ans[i]*solve(t[i].x,t[i].y,n,m)%mod+mod)%mod;
        }
        printf("Case #%d: %lld\n",cas++,sum);
    }
    return ;
}