20 days team study | Tencent Featured 54.59.61 questions

054 Spiral Matrix

Title description

给定一个包含 m x n 个元素的矩阵（m 行, n 列），请按照顺时针螺旋顺序，返回矩阵中的所有元素。
示例 1:
输入:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
输出: [1,2,3,6,9,8,7,4,5]

Problem solving method

violence

python code

class Solution(object):
    def spiralOrder(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[int]
        """
        if matrix is None or len(matrix) == 0:
            return matrix
        m, n = len(matrix), len(matrix[0])
        return self.get_spiralOrder(matrix, 0, m - 1, 0, n - 1)

    def get_spiralOrder(self, matrix, r_start, r_end, c_start, c_end):
        if r_start > r_end or c_start > c_end:
            return []
        elif r_start == r_end:
            return matrix[r_start][c_start:c_end + 1]
        elif c_start == c_end:
            return [matrix[j][c_end] for j in range(r_start, r_end + 1)]
        curr = matrix[r_start][c_start:c_end + 1] + [matrix[j][c_end] for j in range(r_start + 1, r_end)] +\
                matrix[r_end][c_start:c_end + 1][::-1] +\
                [matrix[j][c_start] for j in reversed(range(r_start + 1, r_end))]
        res = curr + self.get_spiralOrder(matrix, r_start + 1, r_end - 1, c_start + 1, c_end - 1)
        return res

059 Spiral Matrix

Title description

给定一个正整数 n，生成一个包含 1 到 n^2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。
示例:
输入: 3
输出:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

Problem solving method

violence

python code

class Solution(object):
    def generateMatrix(self, n):
        """
        :type n: int
        :rtype: List[List[int]]
        """
        res = [[0] * n for _ in range(n)]
        pos = [0, 0]
        move = (0, 1)
        for index in range(1, n * n + 1):
            res[pos[0]][pos[1]] = index
            if res[(pos[0] + move[0]) % n][(pos[1] + move[1]) % n] > 0:
                # (0, 1) -> (1, 0) -> (0, -1) -> (-1, 0)
                move = (move[1], -1 * move[0])
            pos[0] = pos[0] + move[0]
            pos[1] = pos[1] + move[1]
        return res

if __name__ == '__main__':
    # begin
    s = Solution()
    print s.generateMatrix(2)

061 Rotating Linked List

Title description

# 给定一个链表，旋转链表，将链表每个节点向右移动 k 个位置，其中 k 是非负数。
# 示例 1:
# 输入: 1->2->3->4->5->NULL, k = 2
# 输出: 4->5->1->2->3->NULL
# 解释:
# 向右旋转 1 步: 5->1->2->3->4->NULL
# 向右旋转 2 步: 4->5->1->2->3->NULL

Problem solving method

violence

python code

class Solution(object):
    def rotateRight(self, head, k):
        """
        :type head: ListNode
        :type k: int
        :rtype: ListNode
        """
        if not head or k == 0:
            return head

        slow = fast = head
        length = 1

        while k and fast.next:
            fast = fast.next
            length += 1
            k -= 1

        if k != 0:
            k = (k + length - 1) % length # original k % length
            return self.rotateRight(head, k)
        else:
            while fast.next:
                fast = fast.next
                slow = slow.next
            return self.rotate(head, fast, slow)

    def rotate(self, head, fast, slow):
        fast.next = head
        head = slow.next
        slow.next = None
        return head