POJ 1061 青蛙的约会 扩展欧几里德 Java

典型的利用扩展欧几里德算法求解模线性方程！！！
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import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import java.io.PrintWriter;import java.math.BigInteger;import java.util.Scanner;/** * 题意：中文题，不解析！ * * 分析：典型的模线性方程求解。 * * 解法：①、已知n,m,L,x,y 设步数为 s，由题意得出方程：(ms-ns) % L = y-x *           化简得：(m-n)s ≡ (y-x)(mod L) *       ②、根据扩展欧几里德算法求解模线性方程。 * * @author TinyDolphin */public class Main {    private static BigInteger x;    private static BigInteger y;    // 扩展欧几里德算法    public static BigInteger exGcd(BigInteger a, BigInteger b) {        if (b.compareTo(BigInteger.valueOf(0)) == 0) {            x = BigInteger.valueOf(1);            y = BigInteger.valueOf(0);            return a;        } else {            BigInteger d = exGcd(b, a.mod(b));            BigInteger temp = x;            x = y;            y = temp.subtract(a.divide(b).multiply(y));            return d;        }    }    public static void main(String[] args) {        Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));        PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));        BigInteger X;        BigInteger Y;        BigInteger M;        BigInteger N;        BigInteger L;        BigInteger gcd;        while (in.hasNext()) {            X = in.nextBigInteger();            Y = in.nextBigInteger();            M = in.nextBigInteger();            N = in.nextBigInteger();            L = in.nextBigInteger();            BigInteger b = Y.subtract(X);            BigInteger a = M.subtract(N);            BigInteger n = L;            gcd = exGcd(a, n);            if (b.mod(gcd).compareTo(BigInteger.valueOf(0)) == 0) {                // 扩展欧几里德算法求解模线性方程中的 定理一                x = x.multiply(b.divide(gcd)).mod(n);                // 扩展欧几里德算法求解模线性方程中的 定理二                // 注意：得出的 x 可能是负数，需要求最小的正整数解，所以需要 ((x + n/d ) % n/d                x = x.add(n.divide(gcd)).mod(n.divide(gcd));                out.println(x);            } else {                out.println("Impossible");            }        }        out.flush();    }}