走环概率问题（至今有点迷）--牛客第二场（ Eddy Walker）
思路：
概率结论题，好像属于线性递推，现在也不太懂（lll￢ω￢)
1 #define IOS ios_base::sync_with_stdio(0); cin.tie(0); 2 #include <cstdio>//sprintf islower isupper 3 #include <cstdlib>//malloc exit strcat itoa system("cls") 4 #include <iostream>//pair 5 #include <fstream> 6 #include <bitset> 7 //#include <map> 8 //#include<unordered_map> 9 #include <vector> 10 #include <stack> 11 #include <set> 12 #include <string.h>//strstr substr 13 #include <string> 14 #include <time.h>//srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9; 15 #include <cmath> 16 #include <deque> 17 #include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less 18 #include <vector>//emplace_back 19 //#include <math.h> 20 //#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor 21 #include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare) 22 using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation 23 #define mem(a,b) memset(a,b,sizeof(a)) 24 #define fo(a,b,c) for(a=b;a<=c;++a)//register int i 25 #define fr(a,b,c) for(a=b;a>=c;--a) 26 #define pr printf 27 #define sc scanf 28 void swapp(int &a,int &b); 29 double fabss(double a); 30 int maxx(int a,int b); 31 int minn(int a,int b); 32 int Del_bit_1(int n); 33 int lowbit(int n); 34 int abss(int a); 35 //const long long INF=(1LL<<60); 36 const double E=2.718281828; 37 const double PI=acos(-1.0); 38 const int inf=(1<<29); 39 const double ESP=1e-9; 40 const int mod=(int)1e9+7; 41 const int N=(int)1e6+6; 42 43 long long qpow(long long a,long long b,long long mod) 44 { 45 long long ans; 46 a%=mod; 47 ans=1; 48 while(b!=0) 49 { 50 if(b&1) 51 ans=(ans*a)%mod; 52 b/=2; 53 a=(a*a)%mod; 54 } 55 return ans; 56 } 57 58 int main() 59 { 60 int T; 61 sc("%d",&T); 62 long long ans=1,res; 63 while(T--) 64 { 65 long long n,m; 66 sc("%lld%lld",&n,&m); 67 if(n==1) 68 { 69 res=1; 70 } 71 else 72 { 73 if(m==0) 74 { 75 res=0; 76 } 77 else 78 res=qpow(n-1,mod-2,mod); 79 } 80 ans=ans*res; 81 ans%=mod; 82 pr("%lld\n",ans); 83 } 84 return 0; 85 } 86 87 /**************************************************************************************/ 88 89 int maxx(int a,int b) 90 { 91 return a>b?a:b; 92 } 93 94 void swapp(int &a,int &b) 95 { 96 a^=b^=a^=b; 97 } 98 99 int lowbit(int n) 100 { 101 return n&(-n); 102 } 103 104 int Del_bit_1(int n) 105 { 106 return n&(n-1); 107 } 108 109 int abss(int a) 110 { 111 return a>0?a:-a; 112 } 113 114 double fabss(double a) 115 { 116 return a>0?a:-a; 117 } 118 119 int minn(int a,int b) 120 { 121 return a<b?a:b; 122 }
