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SpiralOrder.java

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package Algorithms;

import java.util.ArrayList;

public class SpiralOrder {

public ArrayList<Integer> spiralOrder(int[][] matrix) {

ArrayList<Integer> result = new ArrayList<Integer>();

// remember such kinds of board.

if (matrix.length == 0 || matrix[0].length == 0) {

return result;

}

spiralOrderhelp(matrix, result, matrix.length, matrix[0].length);

return result;

}

// m, n: the middle m lines and n columns.

public void spiralOrderhelp(int[][] matrix, ArrayList<Integer> result, int m, int n) {

if (m <= 0 || n <= 0) {

return;

}

// setup the begin point.

int lineB = (matrix.length - m)/2;

int colB = (matrix[0].length - n)/2;

int line = lineB;

int col = colB-1; // begin from the first element.

while (col < colB+n-1) {

result.add(matrix[line][++col]);

}

while (line < lineB+m-1) {

result.add(matrix[++line][col]);

}

// eliminate the duplicate calculating.

while (col > colB && line != lineB) {

result.add(matrix[line][--col]);

}

// eliminate the duplicate calculating.

while (line > lineB+1 && col != colB) {

result.add(matrix[--line][col]);

}

spiralOrderhelp(matrix, result, m-2, n-2);

}

public static void main(String[] args) {

int[][] input = {{2,3}};

SpiralOrder test = new SpiralOrder();

ArrayList<Integer> result = test.spiralOrder(input);

System.out.printf(result.toString());

}