HDU - 5698

 1 #include<iostream>
 2 #include<stdio.h>
 3 #include<cstring>
 4 
 5 using namespace std;
 6 
 7 #define LL long long
 8 const int p = 1000000007;
 9 
10 LL quick(LL a, LL b)
11 {
12     LL ans = 1;
13     a %= p;
14     while(b)
15     {
16         if(b & 1)
17         {
18             ans = ans * a % p;
19             b--;
20         }
21         b >>= 1;
22         a = a * a % p;
23     }
24     return ans;
25 }
26 
27 LL C(LL n, LL m)
28 {
29     if(m > n) return 0;
30     LL ans = 1;
31     for(int i=1; i<=m; i++)
32     {
33         LL a = (n + i - m) % p;
34         LL b = i % p;
35         ans = ans * (a * quick(b, p-2) % p) % p;
36     }
37     return ans;
38 }
39 
40 LL Lucas(LL n, LL m)
41 {
42     if(m == 0) return 1;
43     return C(n % p, m % p) * Lucas(n / p, m / p) % p;
44 }
45 
46 int main()
47 {
48     LL n,m;
49     int i;
50     while(~scanf("%lld%lld",&n,&m))
51     {
52         n-=2;m-=2;
53         if(n>m)
54             swap(n,m);
55         printf("%lld\n",Lucas(m+n,n));
56     }
57     return 0;
58 }