Biorhythms

題意：

求解一元線性同余方程組。

 1 #include <cstdio>
 2 #include <cstring>
 3 using namespace std;
 4 const int maxn=1010;
 5 int b[maxn],m[maxn];
 6 int n;
 7 void exgcd(int a,int b,int &d,int &x,int &y){
 8     if(!b){d=a;x=1;y=0;}
 9     else {exgcd(b,a%b,d,y,x);y-=x*(a/b);}
 
10 }
11 //  求解x%m=b
12 int solve(int* b,int* m,int n){
13     int m1=m[0],b1=b[0];;
14     for(int i=1;i<n;i++){
15         int m2=m[i],b2=b[i];
16         int g,x,y;
17         exgcd(m1,m2,g,x,y);
18         int c=b2-b1;
19         if(c%g) return -1;  //無解
20         x=x*(c/g);
21         int r=m2/g;
22         x=(x%r+r)%r;
 
23         b1+=m1*x;
24         m1*=m2/g;
25         b1%=m1;
26     }
27     return (b1%m1+m1-1)%m1+1;  //返回正整數解
28 }
29 
30 int main(){
31     m[0]=23;m[1]=28;m[2]=33;
32     int kase=0;
33     while(scanf("%d",&b[0])){
34         for(int i=1;i<3;i++) scanf("%d",&b[i]);
35         int x;
36         scanf("
 
%d",&x);
37         if(x==-1) break;
38         int ans=solve(b,m,3);
39         ans=(ans-x+21251)%21252+1;
40         printf("Case %d: the next triple peak occurs in %d days.\n",++kase,ans);
41     }
42 }

Biorhythms POJ - 1006