LeetCode_Spiral Matrix

Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
（螺旋式遍历矩阵）

Example:

1. 方向模拟

事先定义四个方向，按照题中的螺旋式的方向在遍历矩阵，过程中遇到边界时不断的修改方向并修改新的边界。具体实现过程如下：

class Solution:
    def spiralOrder(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[int]
        """
        if not matrix:
            return []
        
        m = len(matrix)
        n = len(matrix[0])

        direction = {
            'right': [0, 1],
            'down': [1, 0],
            'left': [0, -1],
            'up': [-1, 0]
        }

        answer = []
        i, j = 0, 0
        direct = 'right'
        left_border, right_border, up_border, down_border = 0, n-1, 0, m-1

        while len(answer) < m * n:
            answer.append(matrix[i][j])

            if i==up_border and j==right_border and direct=='right':
                direct = 'down'
                up_border += 1
            elif i==down_border and j==right_border and direct=='down':
                direct = 'left'
                right_border -= 1
            elif i==down_border and j==left_border and direct=='left':
                direct = 'up'
                down_border -= 1
            elif i==up_border and j==left_border and direct=='up':
                direct = 'right'
                left_border += 1 
            i += direction[direct][0]
            j += direction[direct][1]

        return answer

2. zip函数

在看别人的简单解法中发现用zip不断地旋转矩阵，每次都获得矩阵的第一行就是螺旋式遍历的结果。具体实现方法如下：

class Solution:
    def spiralOrder(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[int]
        """
        answer = []
        while matrix:
            answer += matrix.pop(0)
            matrix = [*zip(*matrix)][::-1]
        return answer