BZOJ-1407: [Noi2002]Savage (扩展欧几里得)

 1 #include "bits/stdc++.h"
 2 using namespace std;
 3 const int MAX=25;
 4 int n,m,C[MAX],P[MAX],L[MAX];
 5 int exgcd(int a,int b,int &x,int &y){
 6     if (b==0) return x=1,y=0,a;
 7     int d=exgcd(b,a%b,x,y);
 8     int t=x; x=y,y=t-a/b*y;
 9     return d;
10 }
11 int main(){
12     freopen ("gcd.in","r",stdin);freopen ("gcd.out","w",stdout);
13     int i,j,a,b,c,d,e,f,x,y;
14     scanf("%d",&n);
15     for (i=1;i<=n;i++) scanf("%d%d%d",C+i,P+i,L+i),m=max(m,C[i]);
16     for (;m<=1e6;m++){
17         bool flag=true;
18         for (i=1;i<=n;i++){
19             for (j=i+1;j<=n;j++){
20                 a=P[i]-P[j],b=m,c=C[j]-C[i];
21                 d=exgcd(a,b,x,y);
22                 if ((c%d)!=0) continue;
23                 x=x*c/d,x=x%(m/d);
24                 if (x<0) x+=abs(m/d);
25                 if (x<=L[i] && x<=L[j]) {flag=false;goto away;}
26             }
27         }
28         away:if (flag) return printf("%d",m),0;
29     }
30 }