#54螺旋矩阵

import java.util.ArrayList;
import java.util.List;

final class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new ArrayList<>();
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) return result;
        int top = 0, bottom = matrix.length - 1;
        int left = 0, right = matrix[0].length - 1;
        while (top <= bottom && left <= right) {
            for (int column = left; column <= right; column++) result.add(matrix[top][column]);
            if (++top > bottom) break;
            for (int row = top; row <= bottom; row++) result.add(matrix[row][right]);
            if (--right < left) break;
            for (int column = right; column >= left; column--) result.add(matrix[bottom][column]);
            if (--bottom < top) break;
            for (int row = bottom; row >= top; row--) result.add(matrix[row][left]);
            left++;
        }
        return result;
    }
}