POJ 1061 青蛙的约会

得到算式 x + z * m - (y + z * n) = k * L

x - y + z  * (m - n) = k * L

即z * (n - m) + k * L = x - y 可以用扩展欧几里德了

/*Accepted 164K 0MS C++ 633B 2012-10-09 23:38:48 */

#include <stdio.h>

#include <string.h>

#include <stdlib.h>



typedef long long LL;



LL extgcd(LL a, LL b, LL &x, LL &y)

{

    if(b == 0) {x = 1; y = 0; return a;}

    LL d = extgcd(b, a % b, x, y);

    LL t = x;

    x = y;

    y = t - a / b * x;

    return d;

}



int main()

{

    LL x, y, m, n, L, t;

    while(scanf("%lld%lld%lld%lld%lld", &x, &y, &m, &n, &L) != EOF)

    {

        LL a = m - n, b = L, c = y - x;

        if(a < 0) a = -a, c = -c;

        LL d = extgcd(a, b, x, y);

        if(m == n || c % d != 0)

            puts("Impossible");

        else

        {

            b /= d, c /= d, t = c * x;

            t = (t % b + b) % b;

            printf("%I64d\n", t);

        }

    }

    return 0;

}