CF #258 E
2014-07-28 17:23:23
1 /************************************************************************* 2 > File Name: e.cpp 3 > Author: Nature 4 > Mail: 564374850@qq.com 5 > Created Time: Mon 28 Jul 2014 12:43:02 PM CST 6 ************************************************************************/ 7 8 #include <cstdio> 9 #include <cstring> 10 #include <cstdlib> 11 #include <cmath> 12 #include <iostream> 13 #include <algorithm> 14 using namespace std; 15 #define LL long long 16 17 LL n,s,f[25]; 18 19 LL Quick_pow(LL x,LL y,LL p){ 20 LL ans = 1; 21 while(y){ 22 if(y & 1) ans = (ans * x) % p; 23 x = (x * x) % p; 24 y >>= 1; 25 } 26 return ans; 27 } 28 29 LL Comb(LL n,LL m,LL p){ 30 if(m > n) 31 return 0; 32 n %= p; 33 LL up = 1,low = 1; 34 for(LL i = 0; i < m; ++i){ 35 up = up * (n - i) % p; 36 low = low * (i + 1) % p; 37 } 38 return up * Quick_pow(low,p - 2,p) % p; //乘法逆元 39 } 40 41 void LAE(){ 42 LL ans = 0; 43 const LL p = 1e9+7; 44 LL tmax = 1 << n; 45 for(LL i = 0; i < tmax; ++i){ 46 LL tag = 1,sum = s; 47 for(LL j = 0; j < n; ++j){ 48 if(i & (1 << j)){ 49 sum -= (f[j] + 1); 50 tag *= -1; 51 } 52 } 53 if(sum < 0) 54 continue; 55 ans += tag * Comb(sum + n - 1,n - 1,p); 56 ans = (ans + p) % p; 57 } 58 printf("%I64d\n",ans); 59 } 60 61 int main(){ 62 scanf("%I64d%I64d",&n,&s); 63 for(LL i = 0; i < n; ++i) 64 scanf("%I64d",&f[i]); 65 LAE(); 66 return 0; 67 }
