LeetCode Spiral Matrix II

原題

將一個正方形矩陣螺旋著填滿遞增的數字。

注意點：

例子：

輸入: n = 3

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

解題思路

這道題跟 Spiral Matrix 正好相反，一個是螺旋著讀出數字，一個是螺旋著寫入數字，而且這道題還要簡單一點，因為形狀固定是正方形的，所以只要控制四條邊不斷向內縮進就可以了。考慮一下奇偶的情況，在奇數的時候要額外加一個中心點。

AC源碼

class Solution(object):
    def generateMatrix(self, n):
        """
        :type n: int
        :rtype: List[List[int]]
        """
        left = top = 0
        right = n - 1
        bottom = n - 1
        num = 1
        result = [[0 for __ in range(n)] for __ in range(n)]
        while left < right and top < bottom:
            for i in range(left, right):
                result[top][i] = num
                num += 1
            for i in range(top, bottom):
                result[i][right] = num
                num += 1
            for i in range(right, left, -1):
                result[bottom][i] = num
                num += 1
            for i in range(bottom, top, -1):
                result[i][left] = num
                num += 1
            left += 1
            right -= 1
            top += 1
            bottom -= 1
        if left == right and top == bottom:
            result[top][left] = num
        return result


if __name__ == "__main__":
    assert Solution().generateMatrix(5) == [[1, 2, 3, 4, 5], [16, 17, 18, 19, 6], [15, 24, 25, 20, 7],
                                            [14, 23, 22, 21, 8], [13, 12, 11, 10, 9]]