Hdu5391 Wilson theorem

Wilson's theorem

Elementary number theory prime when and only if p for Prime: (P-1)! ≡-1 (mod p), but due to factorial

Hdu5391 used this theorem of number theory.

Zball in Tina townTime limit:3000/1500 MS (java/others) Memory limit:262144/262144 K (java/others)
Total submission (s): 276 Accepted Submission (s): 168


Problem Descriptiontina Town was a friendly place. People there care on each of the other.

Tina has a ball called Zball. Zball is magic. It grows larger every day. On the first day, it becomes 1 Time as large as its original size. On the second day,it'll become 2 Times as large as the size on the first day. On the n-th day,it'll become n Times as large as the size on the (n-1)-th Day. Tina want to know it size on the (n-1)-th day modulo n.

Inputthe first line of input contains an integer T , representing the number of cases.

The following T Lines, each line contains an integer n , according to the description.
T ≤ ten 5 ,2≤N≤ ten 9

Outputfor each test case, output an integer representing the answer.
Sample Input

2310

Sample Output

20

Sourcebestcoder Round #51 (Div.2):

the problem is to ask (n?1)! MoD n (n-1)! modn (N?1)!moD N

If nn NFor composite, the answer is obviously 0.

If nnn Is the prime number, then the answer to the Wilson theorem can be< Span class= "Katex-mathml" style= "Position:absolute; padding:0px; border:0px; height:1px; width:1px; Overflow:hidden ">n?1n-1 n 1

Note that there is a trick for nnn = 4

Code:

#include <iostream> #include <cmath> #define LL long long using namespace Std;int t;int n,ans;bool isprime (int m ) {    int i,isqrt= (int) sqrt (m);    BOOL Pd=true;    if (m==2) pd=true;    else if (m%2==0) Pd=false;    else for     (i=3;i<=isqrt;i+=2) {        if (m%i==0) {            pd=false;            break;        }    }    return PD;} int main () {    cin>>t;    while (t--) {        cin>>n;        if (n==4) ans=2;        else if (IsPrime (n)) ans=n-1;        else ans=0;        cout<<ans<<endl;    }    return 0;}

Started to time out, the problem is in the number of judgment prime. We must pay attention to the problem of prime number determination.

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Hdu5391 Wilson theorem