问按螺旋顺序打印二维数组

EN

import java.util.Iterator;

class Pair {
    final int i;
    final int j;

    Pair(int i, int j) {
        this.i = i;
        this.j = j;
    }

    @Override
    public String toString() {
        return "Pair [i=" + i + ", j=" + j + "]";
    }
}


enum Direction {
    N, E, S, W;
}


class SpiralIterator implements Iterator<Pair> {
    private final int r, c;
    int ri, ci;
    int cnt;

    Direction d; // current direction
    int level; // spiral level;

    public SpiralIterator(int r, int c) {
        this.r = r;
        this.c = c;

        d = Direction.E;
        level = 1;
    }

    @Override
    public boolean hasNext() {
        return cnt < r * c;
    }

    @Override
    public Pair next() {
        final Pair p = new Pair(ri, ci);
        switch (d) {
            case E:
                if (ci == c - level) {
                    ri += 1;
                    d = changeDirection(d);
                } else {
                    ci += 1;
                }
                break;

            case S:
                if (ri == r - level) {
                    ci -= 1;
                    d = changeDirection(d);
                } else {
                    ri += 1;
                }
                break;

            case W:
                if (ci == level - 1) {
                    ri -= 1;
                    d = changeDirection(d);
                } else {
                    ci -= 1;
                }
                break;

            case N:
                if (ri == level) {
                    ci += 1;
                    level += 1;
                    d = changeDirection(d);
                } else {
                    ri -= 1;
                }
                break;
        }

        cnt += 1;
        return p;
    }

    private static Direction changeDirection(Direction d) {
        switch (d) {
            case E:
                return Direction.S;
            case S:
                return Direction.W;
            case W:
                return Direction.N;
            case N:
                return Direction.E;
            default:
                throw new IllegalStateException();
        }
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }

}


public class FillMatrix {
    static int[][] fill(int r, int c) {
        final int[][] m = new int[r][c];
        int i = 1;
        final Iterator<Pair> iter = new SpiralIterator(r, c);
        while (iter.hasNext()) {
            final Pair p = iter.next();
            m[p.i][p.j] = i;
            i += 1;
        }
        return m;
    }

    public static void main(String[] args) {
        final int r = 19, c = 19;
        final int[][] m = FillMatrix.fill(r, c);
        for (int i = 0; i < r; i++) {
            for (int j = 0; j < c; j++) {
                System.out.print(m[i][j] + " ");
            }
            System.out.println();
        }
    }
}