LeetCode | Spiral Matrix

題目

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]

You should return [1,2,3,6,9,8,7,4,5].

這題沒用到什麼特別的技巧，就是一層一層來，需要注意一些邊界條件。

代碼

import java.util.ArrayList;

public class SpiralMatrix {
	public ArrayList spiralOrder(int[][] matrix) {
		ArrayList list = new ArrayList();
		if (matrix == null || matrix.length == 0) {
			return list;
		}
		int minRow = 0;
		int minColumn = 0;
		int maxRow = matrix.length - 1;
		int maxColumn = matrix[0].length - 1;
		while (minRow <= maxRow && minColumn <= maxColumn) {
			for (int i = minColumn; i <= maxColumn; ++i) {
				list.add(matrix[minRow][i]);
			}
			for (int i = minRow + 1; i <= maxRow; ++i) {
				list.add(matrix[i][maxColumn]);
			}
			if (minRow != maxRow) {
				for (int i = maxColumn - 1; i >= minColumn; --i) {
					list.add(matrix[maxRow][i]);
				}
			}
			if (minColumn != maxColumn) {
				for (int i = maxRow - 1; i > minRow; --i) {
					list.add(matrix[i][minColumn]);
				}
			}
			++minRow;
			++minColumn;
			--maxRow;
			--maxColumn;
		}
		return list;
	}
}