059--Spiral Matrix II.md

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

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

按照发展的规律也往往是最容易想到的。

class Solution(object):
    def generateMatrix(self, n):
        """
        :type n: int
        :rtype: List[List[int]]
        """
        A = [[0] * n for _ in range(n)]
        i, j, di, dj = 0, 0, 0, 1
        for k in xrange(n*n):
            A[i][j] = k + 1
            if A[(i+di)%n][(j+dj)%n]:
                di, dj = dj, -di
            i += di
            j += dj
        return A