Problem:
Score : 100 points

Problem Statement

There is a simple directed graph G with N vertices, numbered 1, 2, \ldots, N.

For each i and j (1 \leq i, j \leq N), you are given an integer a_{i, j} that represents whether there is a directed edge from Vertex i to j.
If a_{i, j} = 1, there is a directed edge from Vertex i to j; if a_{i, j} = 0, there is not.

Find the number of different directed paths of length K in G, modulo 10^9 + 7.
We will also count a path that traverses the same edge multiple times.

Constraints

All values in input are integers.

1 \leq N \leq 50

1 \leq K \leq 10^{18}

a_{i, j} is 0 or 1.

a_{i, i} = 0

Input

Input is given from Standard Input in the following format:

N K
a_{1, 1} \ldots a_{1, N}
:
a_{N, 1} \ldots a_{N, N}

Output

Print the number of different directed paths of length K in G, modulo 10^9 + 7.

Sample Input 1

4 2
0 1 0 0
0 0 1 1
0 0 0 1
1 0 0 0

Sample Output 1

6

G is drawn in the figure below:

There are six directed paths of length 2:

1 → 2 → 3

1 → 2 → 4

2 → 3 → 4

2 → 4 → 1

3 → 4 → 1

4 → 1 → 2

Sample Input 2

3 3
0 1 0
1 0 1
0 0 0

Sample Output 2

3

G is drawn in the figure below:

There are three directed paths of length 3:

1 → 2 → 1 → 2

2 → 1 → 2 → 1

2 → 1 → 2 → 3

Sample Input 3

6 2
0 0 0 0 0 0
0 0 1 0 0 0
0 0 0 0 0 0
0 0 0 0 1 0
0 0 0 0 0 1
0 0 0 0 0 0

Sample Output 3

1

G is drawn in the figure below:

There is one directed path of length 2:

4 → 5 → 6

Sample Input 4

1 1
0

Sample Output 4

0

Sample Input 5

10 1000000000000000000
0 0 1 1 0 0 0 1 1 0
0 0 0 0 0 1 1 1 0 0
0 1 0 0 0 1 0 1 0 1
1 1 1 0 1 1 0 1 1 0
0 1 1 1 0 1 0 1 1 1
0 0 0 1 0 0 1 0 1 0
0 0 0 1 1 0 0 1 0 1
1 0 0 0 1 0 1 0 0 0
0 0 0 0 0 1 0 0 0 0
1 0 1 1 1 0 1 1 1 0

Sample Output 5

957538352

Be sure to print the count modulo 10^9 + 7.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.NoSuchElementException;
import java.util.function.UnaryOperator;

public class Main {
    public static ModuloArithmetic ma = new ModuloArithmetic(Const.MOD7);
    public static void main(String[] args) {
        Out out = new Out();
        solve(out);
        out.outln();
        out.flush();
        out.close();
    }

    public static void solve(Out out) {
        int n = In.ni();
        long k = In.nl();
        long[][] a = new long[n][n];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                a[i][j] = In.ni();
            }
        }
        SquareMatrix.setModuloArithmetic(ma);
        SquareMatrix sq = new SquareMatrix(a);
        sq = sq.pow(k);
        long ans = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                ans += sq.get(i, j);
            }
        }
        out.append(ma.mod(ans));
    }
}


class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte()) {
            return buffer[ptr++];
        } else {
            return -1;
        }
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
            ptr++;
        }
        return hasNextByte();
    }

    public String next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) {
            throw new NumberFormatException();
        }
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
}

class ModuloArithmetic {
    public final long MOD;
    private long[] fact;
    private long[] pow;

    /**
     * support modulo p arithmetic
     * 
     * @param p p s.t. p is a prime number.
     */
    public ModuloArithmetic(long p) {
        this.MOD = p;
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ x = a mod p.
     * 
     * @param a
     * @return x s.t. 0 <= x < MOD /\ x = a mod p.
     */
    public long mod(long a) {
        a %= MOD;
        return a < 0 ? a + MOD : a;
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ x = a_1 + 1_2 + ... + a_k mod p.
     * 
     * @param a
     * @return x s.t. 0 <= x < MOD /\ x = a_1 + 1_2 + ... + a_k mod p.
     */
    public long sum(long... a) {
        long ret = 0;
        for (long c : a) ret += c;
        return mod(ret);
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ x = a + b mod p.
     * 
     * @param a
     * @param b
     * @return x s.t. 0 <= x < MOD /\ x = a + b mod p.
     */
    public long add(long a, long b) {
        long s = a + b;
        return s < 0 ? s + MOD : s >= MOD ? s - MOD : s;
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ x = a - b mod p.
     * 
     * @param a
     * @param b
     * @return x s.t. 0 <= x < MOD /\ x = a - b mod p.
     */
    public long sub(long a, long b) {
        long s = a - b;
        return s < 0 ? s + MOD : s >= MOD ? s - MOD : s;
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ x = a_1 * 1_2 * ... * a_k mod p.
     * 
     * @param a
     * @return x s.t. 0 <= x < MOD /\ x = a_1 * 1_2 * ... * a_k mod p.
     */
    public long prod(long... a) {
        long ret = 1;
        for (long c : a) {
            ret = (ret * c) % MOD;
        }
        return ret < 0 ? ret + MOD : ret;
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ x = a * b mod p.
     * 
     * @param a
     * @param b
     * @return x s.t. 0 <= x < MOD /\ x = a * b mod p.
     */
    public long mul(long a, long b) {
        return mod(a * b);
    }

    /**
     * Calculate x s.t. 0 <= x < MOD /\ b * x = a mod p.
     * 
     * @param a
     * @param b
     * @return x s.t. 0 <= x < MOD /\ b * x = a mod p.
     */
    public long div(long a, long b) {
        return mul(a, inv(b));
    }

    /**
     * Calculate the value b s.t. a*b mod MOD = 1.
     * 
     * @param a
     * @return inverse of a
     */
    public long inv(long a) {
        long b = MOD;
        long u = 1, v = 0;
        while (b >= 1) {
            long t = a / b;
            a -= t * b;
            long tmp1 = a; a = b; b = tmp1;
            u -= t * v;
            long tmp2 = u; u = v; v = tmp2;
        }
        return mod(u);
    }

    /**
     * Calculate the permutation nPr.
     * 
     * @param n
     * @param r
     * @return nPr
     */
    public long perm(long n, long r) {
        if (n < r) {
            return 0;
        }
        if (fact != null && n <= fact.length) {
            return div(fact[(int) n], fact[(int) (n - r)]);
        }
        long ret = 1;
        for (long i = n; i > n - r; i--) {
            ret = mul(ret, i);
        }
        return ret;
    }

    /**
     * Calculate the combination nCr.
     * 
     * @param n
     * @param r
     * @return nCr
     */
    public long comb(long n, long r) {
        if (n < r) {
            return 0;
        }
        if (fact != null && n <= fact.length) {
            return div(fact[(int) n], mul(fact[(int) (n - r)], fact[(int) r]));
        }
        r = Math.min(r, n - r);
        long res = 1;
        for (long d = 1; d <= r; d++) {
            res = div(mul(res, n--), d);
        }
        return res;
    }
    
    /**
     * call this method after building factorial array.
     * 
     * @param n
     * @return n! mod p
     */
    public long fact(int n) {
        return fact[n];
    }

    /**
     * call this nethod after building power array.
     * 
     * @param n
     * @return (base)^n
     */
    public long pow(int n) {
        return pow[n];
    }

    /**
     * Calculate a^b (mod {@code MOD}) in O(log b) time.
     * 
     * @param a base
     * @param b index
     * @return a^b (mod {@code MOD})
     */
    public long pow(long a, long b) {
        if (b == 0) {
            return 1;
        }
        long half = pow(a, b >> 1);
        if ((a & 1) == 0) {
            return mul(half, half);
        } else {
            return prod(half, half, a);
        }
    }

    /**
     * build factorial array from 0 to n (closed)
     * 
     * @param n
     */
    public void buildFactorial(int n) {
        this.fact = new long[n + 1];
        for (int i = 0; i <= n; i++) {
            if (i <= 1) {
                fact[i] = 1;
            } else {
                fact[i] = mul(fact[i - 1], i);
            }
        }
    }

    /**
     * build power array based on a from 0 to n (closed)
     * 
     * @param a base of power
     * @param n
     */
    public void buildPower(long a, int n) {
        if (a == 2) {
            buildPower(n);
        } else {
            this.pow = new long[n + 1];
            for (int i = 0; i <= n; i++) {
                if (i == 0) {
                    pow[i] = 1;
                } else {
                    pow[i] = mul(pow[i - 1], a);
                }
            }
        }
    }

    /**
     * build power array based on 2 from 0 to n (closed)
     * 
     * @param n
     */
    public void buildPower(int n) {
        this.pow = new long[n + 1];
        for (int i = 0; i <= n; i++) {
            if (i == 0) {
                pow[i] = 1;
            } else {
                pow[i] = pow[i - 1] << 1;
                if (pow[i] >= MOD) {
                    pow[i] -= MOD;
                }
            }
        }
    }
}


class Out {
    private StringBuilder sb = new StringBuilder();
    private PrintWriter w = new PrintWriter(System.out);

    public Out() {
    }

    public void append(int v) {
        sb.append(v);
    }

    public void append(long v) {
        sb.append(v);
    }

    public void append(char c) {
        sb.append(c);
    }

    public void append(double v) {
        sb.append(v);
    }

    public void append(char[] c) {
        sb.append(c);
    }

    public void append(String s) {
        sb.append(s);
    }

    public void append(Object e) {
        sb.append(e);
    }

    public void append(int[] a, String sep) {
        for (int i = 0; i < a.length; i++) {
            append(a[i]);
            if (i < a.length - 1) {
                append(sep);
            }
        }
    }

    public void append(long[] a, String sep) {
        for (int i = 0; i < a.length; i++) {
            append(a[i]);
            if (i < a.length - 1) {
                append(sep);
            }
        }
    }

    public void append(char[] a, String sep) {
        for (int i = 0; i < a.length; i++) {
            append(a[i]);
            if (i < a.length - 1) {
                append(sep);
            }
        }
    }

    public void append(double[] a, String sep) {
        for (int i = 0; i < a.length; i++) {
            append(a[i]);
            if (i < a.length - 1) {
                append(sep);
            }
        }
    }

    public void append(char[][] c, String sep) {
        for (int i = 0; i < c.length; i++) {
            append(c[i]);
            if (i < c.length - 1) {
                append(sep);
            }
        }
    }

    public void append(String[] a, String sep) {
        for (int i = 0; i < a.length; i++) {
            append(a[i]);
            if (i < a.length - 1) {
                append(sep);
            }
        }
    }

    public void append(Object[] a, String sep) {
        for (int i = 0; i < a.length; i++) {
            append(a[i]);
            if (i < a.length - 1) {
                append(sep);
            }
        }
    }

    public void out() {
        w.print(sb);
        clearBuilder();
    }

    public void outln() {
        w.println(sb);
        clearBuilder();
    }

    public void print(int v) {
        w.print(v);
    }

    public void print(long v) {
        w.print(v);
    }

    public void print(char c) {
        w.print(c);
    }

    public void print(double v) {
        w.print(v);
    }

    public void print(String s) {
        w.print(s);
    }

    public void print(Object e) {
        w.print(e);
    }

    public void print(String sep, int... a) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < a.length; i++) {
            s.append(a[i]);
            if (i < a.length - 1) {
                s.append(sep);
            }
        }
        print(s);
    }

    public void print(String sep, long... a) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < a.length; i++) {
            s.append(a[i]);
            if (i < a.length - 1) {
                s.append(sep);
            }
        }
        print(s);
    }

    public void print(String sep, char... a) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < a.length; i++) {
            s.append(a[i]);
            if (i < a.length - 1) {
                s.append(sep);
            }
        }
        print(s);
    }

    public void print(String sep, double... a) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < a.length; i++) {
            s.append(a[i]);
            if (i < a.length - 1) {
                s.append(sep);
            }
        }
        print(s);
    }

    public void print(String sep, String... a) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < a.length; i++) {
            s.append(a[i]);
            if (i < a.length - 1) {
                s.append(sep);
            }
        }
        print(s);
    }

    public void print(String sep, Object... a) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < a.length; i++) {
            s.append(a[i]);
            if (i < a.length - 1) {
                s.append(sep);
            }
        }
        print(s);
    }

    public void println() {
        w.println();
    }

    public void println(int v) {
        w.println(v);
    }

    public void println(long v) {
        w.println(v);
    }

    public void println(double v) {
        w.println(v);
    }

    public void println(char c) {
        w.println(c);
    }

    public void println(String s) {
        w.println(s);
    }

    public void println(Object e) {
        w.println(e);
    }

    public void println(String sep, int... a) {
        print(sep, a);
        println();
    }

    public void println(String sep, long... a) {
        print(sep, a);
        println();
    }

    public void println(String sep, double... a) {
        print(sep, a);
        println();
    }

    public void println(String sep, char... a) {
        print(sep, a);
        println();
    }

    public void println(String sep, String... a) {
        print(sep, a);
        println();
    }

    // public void println(String sep, Object... a) {
    //     print(sep, a);
    //     println();
    // }

    public void flush() {
        w.flush();
    }

    public void close() {
        w.close();
    }

    public void clearBuilder() {
        sb = new StringBuilder();
    }

    public void reverse() {
        sb.reverse();
    }

    public void delete(int start, int end) {
        sb.delete(start, end);
    }

    public void delete(int length) {
        sb.delete(sb.length() - length, sb.length());
    }

    public int length() {
        return sb.length();
    }
}

class Const {
    public static final long MOD7 = 1_000_000_007;
    public static final long MOD9 = 1_000_000_009;
    public static final long MOD99 = 998_244_353;

    public static final long LINF = 1_000_000_000_000_000_000l;
    public static final int IINF = 1_000_000_000;
    public static final double DINF = 1e150;

    public static final double DELTA = 0.000_000_000_1;
    public static final double LDELTA = 0.000_001;

    public static final String YES = "YES";
    public static final String NO = "NO";
    public static final String Yes = "Yes";
    public static final String No = "No";
    public static final String POSSIBLE = "POSSIBLE";
    public static final String IMPOSSIBLE = "IMPOSSIBLE";
    public static final String Possible = "Possible";
    public static final String Impossible = "Impossible";

    public static final int[] dx8 = {1, 0, -1, 0, 1, -1, -1, 1};
    public static final int[] dy8 = {0, 1, 0, -1, 1, 1, -1, -1};
    public static final int[] dx = {1, 0, -1, 0};
    public static final int[] dy = {0, 1, 0, -1};

    private Const(){}
}


class In {
    public static final FastScanner fsc = new FastScanner();

    public static int ni() {
        return fsc.nextInt();
    }

    public static int[] ni(int n) {
        int[] a = new int[n];
        Arrays.setAll(a, i -> fsc.nextInt());
        return a;
    }

    public static int[][] ni(int n, int m) {
        int[][] a = new int[n][m];
        Arrays.setAll(a, i -> ni(m));
        return a;
    }

    public static long nl() {
        return fsc.nextLong();
    }

    public static long[] nl(int n) {
        long[] a = new long[n];
        Arrays.setAll(a, i -> fsc.nextLong());
        return a;
    }

    public static long[][] nl(int n, int m) {
        long[][] a = new long[n][m];
        Arrays.setAll(a, i -> nl(m));
        return a;
    }

    public static char[] nc() {
        return fsc.next().toCharArray();
    }

    public static char[][] nc(int n, int m) {
        char[][] c = new char[n][m];
        Arrays.setAll(c, i -> nc());
        return c;
    }

    public static double nd() {
        return fsc.nextDouble();
    }

    public static double[] nd(int n) {
        double[] a = new double[n];
        Arrays.setAll(a, i -> nd());
        return a;
    }

    public static double[][] nd(int n, int m) {
        double[][] a = new double[n][m];
        Arrays.setAll(a, i -> nd(m));
        return a;
    }

    public static String ns() {
        return fsc.next();
    }

    public static String[] ns(int n) {
        String[] s = new String[n];
        Arrays.setAll(s, i -> ns());
        return s;
    }

    public static boolean[][] inputGrid(int h, int w, char truechar) {
        boolean[][] grid = new boolean[h][w];
        for (int i = 0; i < h; i++) {
            char[] s = fsc.next().toCharArray();
            for (int j = 0; j < w; j++) {
                grid[i][j] = s[j] == truechar;
            }
        }
        return grid;
    }
}

class SquareMatrix extends Matrix {
    protected final int n;

    public SquareMatrix(int n) {
        super(n, n);
        this.n = n;
    }

    public SquareMatrix(int n, long init) {
        super(n, n, init);
        this.n = n;
    }

    public SquareMatrix(long[][] a) {
        super(a);
        this.n = a.length;
    }

    public SquareMatrix(long[] a, int n) {
        super(a, n, n);
        this.n = n;
    }

    public SquareMatrix prod(SquareMatrix b) {
        long[] ret = new long[n * n];
        for (int i = 0; i < n; i++) {
            for (int k = 0; k < n; k++) {
                for (int j = 0; j < n; j++) {
                    ret[i * n + j] = ma.add(ret[i * n + j], ma.mul(a[i * n + k], b.a[k * n + j]));
                }
            }
        }
        return new SquareMatrix(ret, n);
    }

    public SquareMatrix pow(long b) {
        if (b == 1) {
            return this;
        }
        SquareMatrix half = pow(b >> 1);
        SquareMatrix hh = (SquareMatrix) half.prod(half);
        return (b & 1) == 0 ? hh : (SquareMatrix) hh.prod(this);
    }

    public static SquareMatrix e(int n) {
        long[] a = new long[n * n];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                a[i * n + j] = i == j ? 1 : 0;
            }
        }
        return new SquareMatrix(a, n);
    }
}

class Matrix {
    protected static ModuloArithmetic ma;

    protected final int r;
    protected final int c;

    protected long[] a;

    public Matrix(int r, int c) {
        this.r = r;
        this.c = c;
        this.a = new long[r * c];
    }

    public Matrix(int r, int c, long init) {
        this.r = r;
        this.c = c;
        this.a = ArrayUtil.filledArray(init, r * c);
    }

    public Matrix(long[][] a) {
        this.r = a.length;
        this.c = a[0].length;
        this.a = new long[r * c];
        for (int i = 0; i < r; i++) {
            for (int j = 0; j < c; j++) {
                this.a[i * this.c + j] = a[i][j];
            }
        }
    }

    protected Matrix(long[] a, int r, int c) {
        this.r = r;
        this.c = c;
        this.a = a.clone();
    }

    public static void setModuloArithmetic(ModuloArithmetic ma) {
        Matrix.ma = ma;
    }

    public long get(int i, int j) {
        return a[i * c + j];
    }

    public Matrix prod(Matrix b) {
        long[] ret = new long[r * b.c];
        for (int i = 0; i < r; i++) {
            for (int k = 0; k < c; k++) {
                for (int j = 0; j < b.c; j++) {
                    ret[i * b.c + j] = ma.add(ret[i * b.c + j], ma.mul(a[i * c + k], b.a[k * b.c + j]));
                }
            }
        }
        return new Matrix(ret, r, b.c);
    }
}


class ArrayUtil {
    public static int[] compress(long[] a) {
        int n = a.length;
        HashSet<Long> set = new HashSet<>();
        for (long e : a) {
            set.add(e);
        }
        ArrayList<Long> sorted = new ArrayList<>(set);
        int size = sorted.size();
        Collections.sort(sorted);
        int[] compress = new int[n];
        for (int i = 0; i < n; i++) {
            int l = 0, r = size;
            while (r - l > 1) {
                int m = l + (r - l) / 2;
                if (sorted.get(m) <= a[i]) {
                    l = m;
                } else {
                    r = m;
                }
            }
            compress[i] = l + 1;
        }
        return compress;
    }

    /**
     * destructive methods
     */

    public static void swap(int[] a, int u, int v) {
        int tmp = a[u];
        a[u] = a[v];
        a[v] = tmp;
    }

    public static void swap(long[] a, int u, int v) {
        long tmp = a[u];
        a[u] = a[v];
        a[v] = tmp;
    }

    public static void reverse(int[] a, int begin, int end) {
        for (int i = begin; i < begin + (end - begin) / 2; i++) {
            swap(a, i, begin + end - i - 1);
        }
    }

    public static void reverse(int[] a) {
        reverse(a, 0, a.length);
    }

    public static void reverse(long[] a, int begin, int end) {
        for (int i = begin; i < begin + (end - begin) / 2; i++) {
            swap(a, i, begin + end - i - 1);
        }
    }

    public static void reverse(long[] a) {
        reverse(a, 0, a.length);
    }

    public static void revSort(int[] a) {
        Arrays.sort(a);
        reverse(a);
    }

    public static void revSort(long[] a) {
        Arrays.sort(a);
        reverse(a);
    }

    public static void sort(int[][] a, int sortIndex) {
        Arrays.sort(a, (u, v) -> u[sortIndex] - v[sortIndex]);
    }

    public static void sort(int[][] a) {
        sort(a, 0);
    }

    public static void sort(long[][] a, int sortIndex) {
        Arrays.sort(a, (u, v) -> Long.compare(u[sortIndex], v[sortIndex]));
    }

    public static void sort(long[][] a) {
        sort(a, 0);
    }

    public static void revSort(int[][] a, int sortIndex) {
        Arrays.sort(a, (u, v) -> v[sortIndex] - u[sortIndex]);
    }

    public static void revSort(int[][] a) {
        revSort(a, 0);
    }

    public static void revSort(long[][] a, int sortIndex) {
        Arrays.sort(a, (u, v) -> Long.compare(v[sortIndex], u[sortIndex]));
    }

    public static void revSort(long[][] a) {
        revSort(a, 0);
    }

    /**
     * permutation
     */

    public static int[] nextPermutation(int[] a) {
        int[] ret = a.clone();
        int n = ret.length;
        for (int i = n - 1; i >= 1; i--) {
            if (ret[i] > ret[i - 1]) {
                int fail = n, pass = i;
                while (fail - pass > 1) {
                    int mid = pass + (fail - pass) / 2;
                    if (ret[mid] > ret[i - 1]) {
                        pass = mid;
                    } else {
                        fail = mid;
                    }
                }
                swap(ret, pass, i - 1);
                reverse(ret, i, n);
                return ret;
            }
        }
        return null;
    }

    public static int[] predPermutation(int[] a) {
        int[] ret = a.clone();
        int n = ret.length;
        for (int i = n - 1; i >= 1; i--) {
            if (ret[i] < ret[i - 1]) {
                int fail = n, pass = i;
                while (fail - pass > 1) {
                    int mid = pass + (fail - pass) / 2;
                    if (ret[mid] < ret[i - 1]) {
                        pass = mid;
                    } else {
                        fail = mid;
                    }
                }
                swap(ret, pass, i - 1);
                reverse(ret, i, n);
                return ret;
            }
        }
        return null;
    }

    /**
     * 
     */

    public static int[] map(UnaryOperator<Integer> op, int[] a) {
        int[] b = new int[a.length];
        for (int i = 0; i < a.length; i++) {
            b[i] = op.apply(a[i]);
        }
        return b;
    }

    public static long[] map(UnaryOperator<Long> op, long[] a) {
        long[] b = new long[a.length];
        for (int i = 0; i < a.length; i++) {
            b[i] = op.apply(a[i]);
        }
        return b;
    }

    public static <T> T[] map(UnaryOperator<T> op, T[] a) {
        @SuppressWarnings("unchecked")
        T[] b = (T[]) new Object[a.length];
        for (int i = 0; i < a.length; i++) {
            b[i] = op.apply(a[i]);
        }
        return b;
    }

    public static int[][] transpose(int[][] a) {
        int n = a.length;
        int m = a[0].length;
        int[][] ret = new int[m][n];
        for (int j = 0; j < m; j++) {
            for (int i = 0; i < n; i++) {
                ret[j][i] = a[i][j];
            }
        }
        return ret;
    }

    public static long[][] transpose(long[][] a) {
        int n = a.length;
        int m = a[0].length;
        long[][] ret = new long[m][n];
        for (int j = 0; j < m; j++) {
            for (int i = 0; i < n; i++) {
                ret[j][i] = a[i][j];
            }
        }
        return ret;
    }

    /**
     * comparation
     */

    public static int compare(int[] a, int[] b) {
        for (int i = 0; i < a.length; i++) {
            if (i >= b.length) {
                return -1;
            } else if (a[i] > b[i]) {
                return 1;
            } else if (a[i] < b[i]) {
                return -1;
            }
        }
        if (a.length < b.length) {
            return 1;
        } else {
            return 0;
        }
    }

    public static int compare(long[] a, long[] b) {
        for (int i = 0; i < a.length; i++) {
            if (i >= b.length) {
                return -1;
            } else if (a[i] > b[i]) {
                return 1;
            } else if (a[i] < b[i]) {
                return -1;
            }
        }
        if (a.length < b.length) {
            return 1;
        } else {
            return 0;
        }
    }

    public static boolean equals(int[] a, int[] b) {
        return compare(a, b) == 0;
    }

    public static boolean equals(long[] a, long[] b) {
        return compare(a, b) == 0;
    }

    /**
     * initialize methods
     */

    public static int[] filledArray(int init, int n) {
        int[] ret = new int[n];
        Arrays.fill(ret, init);
        return ret;
    }

    public static int[][] filledArray(int init, int n, int m) {
        int[][] ret = new int[n][m];
        for (int i = 0; i < n; i++) {
            Arrays.fill(ret[i], init);
        }
        return ret;
    }

    public static long[] filledArray(long init, int n) {
        long[] ret = new long[n];
        Arrays.fill(ret, init);
        return ret;
    }

    public static long[][] filledArray(long init, int n, int m) {
        long[][] ret = new long[n][m];
        for (int i = 0; i < n; i++) {
            Arrays.fill(ret[i], init);
        }
        return ret;
    }
}