Spiral Matrix

spiral_order.py

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

Examples:
Input:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
Output: [1,2,3,6,9,8,7,4,5]

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]
"""

def spiralOrder(matrix):
    """
    :type matrix: List[List[int]]
    :rtype: List[int]
    """
    if not matrix: return []
    m, n = len(matrix), len(matrix[0])
    startRow, endRow = 0, m-1
    startCol, endCol = 0, n-1
    result = []
    count = m * n
    while startRow <= endRow and startCol <= endCol:
        for i in range(startCol, endCol+1):
            result.append(matrix[startRow][i])
            count -= 1
        if count == 0: break
        startRow += 1
        for i in range(startRow, endRow+1):
            result.append(matrix[i][endCol])
            count -= 1
        if count == 0: break
        endCol -= 1
        for i in range(endCol, startCol-1, -1):
            result.append(matrix[endRow][i])
            count -= 1
        if count == 0: break
        endRow -= 1
        for i in range(endRow, startRow-1, -1):
            result.append(matrix[i][startCol])
            count -= 1
        if count == 0: break
        startCol += 1
    return result