hdu 2604 Queuing 递推/DP 矩阵快速幂 Trie数辅助

过于傻气的递推公式！
状态傻傻分不清楚
写矩阵乘法，混淆了左乘与右乘。

引用一个类比字符串模式匹配的trie树的应用：

/**
 * 2015年7月14日 下午4:51:05
 * PrjName:hdu2604
 * @ Semprathlon
 */
import java.io.*;

class Matrix {
    int n, m, mod;
    int[][] dat;

    Matrix(int n, int m, int mod) {
        this.n = n;
        this.m = m;
        this.mod = mod;
        this.dat = new int[n][m];
    }

    Matrix(Matrix mat) {
        this.n = mat.n;
        this.m = mat.m;
        this.mod = mat.mod;
        this.dat = new int[n][m];
        for (int i = 0; i < mat.n; i++)
            for (int j = 0; j < mat.m; j++)
                this.dat[i][j] = mat.dat[i][j];
    }

    static Matrix one(Matrix mat) {
        Matrix res = new Matrix(mat.n, mat.m, mat.mod);
        for (int i = 0; i < Math.min(mat.n, mat.m); i++)
            res.dat[i][i] = 1;
        return res;
    }

    Matrix add(Matrix c) {
        Matrix res = new Matrix(this);
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++) {
                res.dat[i][j] += c.dat[i][j];
                res.dat[i][j] %= mod;
            }
        return res;
    }

    Matrix mul(Matrix c) {
        Matrix res = new Matrix(this.n, c.m, mod);
        for (int i = 0; i < this.n; i++)
            for (int j = 0; j < c.m; j++)
                for (int k = 0; k < this.m; k++) {
                    res.dat[i][j] += this.dat[i][k] * c.dat[k][j];
                    res.dat[i][j] %= mod;
                }

        return res;
    }

    Matrix pow(int m) {
        Matrix n = new Matrix(this);
        Matrix res = Matrix.one(n);
        while (m > 0) {
            if ((m & 1) > 0)
                res = res.mul(n);
            n = n.mul(n);
            m >>= 1;
        }
        return res;
    }
}

public class Main {
    static Matrix mat, p;

    static void init(int mod) {
        mat = new Matrix(4, 1, mod);
        mat.dat = new int[][] { { 9 }, { 6 }, { 4 }, { 2 } };
        p = new Matrix(4, 4, mod);
        p.dat = new int[][] { { 1, 0, 1, 1 }, { 1, 0, 0, 0 }, { 0, 1, 0, 0 },
                { 0, 0, 1, 0 } };
    }

    static int solve(int l, int m) {
        mat = p.pow(l - 4).mul(mat);
        if (l > 4)
            return mat.dat[0][0];
        else if (l > 0)
            return mat.dat[4 - l][0];
        return 0;
    }

    public static void main(String[] args) throws IOException {
        StreamTokenizer in = new StreamTokenizer(new BufferedReader(
                new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        while (in.nextToken() != StreamTokenizer.TT_EOF) {
            int l = (int) in.nval;
            in.nextToken();
            int m = (int) in.nval;
            init(m);
            out.println(solve(l, m) % m);    
        }
        out.flush();
        out.close();
    }
}