【LeetCode-算法】54. 螺旋矩阵（Java实现）

题目

给定一个包含 m x n 个元素的矩阵（m 行, n 列），请按照顺时针螺旋顺序，返回矩阵中的所有元素。

示例 1:

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

示例 2:

输入:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
输出: [1,2,3,4,8,12,11,10,9,5,6,7]

代码实现

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 rowNum = matrix.length, colNum = matrix[0].length;
        int top = 0, right = colNum - 1, bottom = rowNum - 1, left = 0;

        while (result.size() < rowNum * colNum) {
            // from left to right
            for (int col = left; col <= right; col++) {
                result.add(matrix[top][col]);
            }
            top++;

            // from top to buttom
            if (result.size() < rowNum * colNum) {
                for (int row = top; row <= bottom; row++) {
                    result.add(matrix[row][right]);
                }
                right--;
            }

            // from right to left
            if (result.size() < rowNum * colNum) {
                for (int row = right; row >= left; row--) {
                    result.add(matrix[bottom][row]);
                }
                bottom--;
            }

            // from buttom to top
            if (result.size() < rowNum * colNum) {
                for (int col = bottom; col >= top; col--) {
                    result.add(matrix[col][left]);
                }
                left++;
            }
        }
        return result;
    }
}