LeetCode 59. Spiral Matrix II.jpg
LeetCode 59. Spiral Matrix II
Description
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 ]
]
描述
给定正整数n，以螺旋顺序生成填充有从1到n2的元素的方阵。
思路
- 此题目同第48题Rotate Image，第54题Spiral Matrix做法类似.第48题解析在这里，第54题解析在这里.
- 同样，我们维护四个指针，rowtop：指向第一行，rowbot：指向最后一行，coleft:指向第一列，colright:指向最后一列。我们另外维护一个num用来记录当前位置填的值.
class Solution:
def generateMatrix(self, n):
"""
:type n: int
:rtype: List[List[int]]
"""
num = 1
# 初始化结果数组，每个位置都初始化为0
res = [[0 for _ in range(n)] for _ in range(n)]
rowtop, coleft, rowbot, colright = 0, 0, n-1, n-1
while rowbot > rowtop and coleft < colright:
# 填第一行
for i in range(coleft, colright):
res[rowtop][i] = num
num += 1
# 填最后一列
for i in range(rowtop, rowbot):
res[i][colright] = num
num += 1
# 填最后一列
for i in range(colright, coleft, -1):
res[rowbot][i] = num
num += 1
# 填第一列
for i in range(rowbot, rowtop, -1):
res[i][coleft] = num
num += 1
# 进入下一层
rowtop += 1
rowbot -= 1
coleft += 1
colright -= 1
# 如果是奇数行，则最后一行需要单独填写
if n % 2:
for i in range(coleft, colright+1):
res[rowtop][i] = num
num += 1
return res
