pku1006 Biorhythms

http://poj.org/problem?id=1006

数论，中国剩余定理

#include <stdio.h>

int extend_gcd(int a, int b, int &x, int &y)
{
    if(b == 0)
    {
        x = 1;
        y = 0;
        return a;
    }
    int r = extend_gcd(b, a%b, y, x);
    y -= x*(a/b);
    return r;
}

int CRT(int a[], int m[], int n)
{
    int M = 1;
    for(int i=0; i<n; i++)
    {
        M *= m[i];
    }
    int ret = 0;
    for(int i=0; i<n; i++)
    {
        int x, y;
        int tm = M/m[i];
        extend_gcd(tm, m[i], x, y);
        ret = (ret + tm*x*a[i])%M;
    }
    return (ret+M)%M;
}

int main()
{
    int cases, d, i, r;
    int a[3], m[3] = {23, 28, 33};
    cases = 0;
    while(scanf("%d%d%d%d", &a[0], &a[1], &a[2], &d), a[0]+1||a[1]+1||a[2]+1||d+1)
    {
        cases ++;
        r = CRT(a, m, 3);
        r -= d;
        r += 21252;
        r %= 21252;
        if(r == 0)
        {
            r = 21252;
        }
        printf("Case %d: the next triple peak occurs in %d days.\n", cases, r);
    }
    return 0;
}