剑指Offer-Python(16-20)

16、合并另个排序链表

# -*- coding:utf-8 -*-
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None


class Solution:
    # 返回合并后列表
    def Merge(self, pHead1, pHead2):
        # write code here
        p1 = pHead1
        p2 = pHead2
        p = ListNode(0)
        pNew = p
        while p1 and p2:
            if p1.val <= p2.val:
                p.next = p1
                p = p.next
                p1 = p1.next
            else:
                p.next = p2
                p = p.next
                p2 = p2.next
        if not p1:
            p.next = p2
        elif not p2:
            p.next = p1
        return pNew.next


head1 = ListNode(1)
t1 = ListNode(3)
head1.next = t1
t2 = ListNode(5)
t1.next = t2
t2.next = None

head2 = ListNode(2)
t1 = ListNode(4)
head2.next = t1
t2 = ListNode(6)
t1.next = t2
t2.next = None

s = Solution()
print(s.Merge(head1, head2).next.val)

17、树的子结构

递归

# -*- coding:utf-8 -*-
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution:
    def HasSubtree(self, root1, root2):
        # write code here
        if not root1 or not root1:
            return False
        return self.doesTreeHashTree2(root1, root2) or self.HasSubtree(root1.right, root2) or self.HasSubtree(
            root1.left, root2)

    def doesTreeHashTree2(self, root1, root2):
        if not root2:
            return True
        if not root1:
            return False
        if root1.val != root2.val:
            return False
        return self.doesTreeHashTree2(root1.left, root2.left) and self.doesTreeHashTree2(root1.right, root2.right)


s = Solution()
tree1 = TreeNode(1)
t1 = TreeNode(2)
t2 = TreeNode(3)
t3 = TreeNode(4)
t4 = TreeNode(5)
tree1.left = t1
tree1.right = t2
t1.left = t3
t1.right = t4

tree2 = TreeNode(2)
t3 = TreeNode(4)
t4 = TreeNode(5)
tree2.left = t3
tree2.right = t4

print(s.HasSubtree(tree1, tree2))

18、二叉树的镜像

递归

# -*- coding:utf-8 -*-
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution:
    # 返回镜像树的根节点
    def Mirror(self, root):
        # write code here
        if not root:
            return
        if not root.left and not root.right:
            return
        temp = root.left
        root.left = root.right
        root.right = temp
        if root.left:
            self.Mirror(root.left)
        elif root.right:
            self.Mirror(root.right)


s = Solution()
tree1 = TreeNode(1)
t1 = TreeNode(2)
t2 = TreeNode(3)
t3 = TreeNode(4)
t4 = TreeNode(5)
tree1.left = t1
tree1.right = t2
t1.left = t3
t1.right = t4

s.Mirror(tree1)
print(tree1.right.right.val)

19、顺时针打印矩阵

# -*- coding:utf-8 -*-
class Solution:
    # matrix类型为二维列表，需要返回列表
    def printMatrix(self, matrix):
        # write code here
        row = len(matrix)
        con = len(matrix[0])
        cir = 0
        t = []
        while row > 2 * cir and con > 2 * cir:
            for i in range(cir, con - cir):  # 右
                t.append(matrix[cir][i])
            if cir < row - cir - 1:  # 下
                for i in range(cir + 1, row - cir):
                    t.append(matrix[i][con - cir - 1])
            if con - cir - 1 > cir and row - cir - 1 > cir:  # 左
                for i in range(con - cir - 2, cir-1, -1):
                    t.append(matrix[row - cir - 1][i])
            if cir < con - cir - 1 and cir < row - cir - 2:  # 下
                for i in range(row - cir - 2, cir, -1):
                    t.append(matrix[i][cir])
            cir += 1
        return t


s = Solution()
a = [[1, 2, 3, 4],
     [5, 6, 7, 8],
     [9, 10, 11, 12],
     [13, 14, 15, 16]]
t = s.printMatrix(a)
print(t)

20、包含min函数的栈

要求min函数时间复杂度为O(1)，因此增加辅助栈存  “当前最小元素“

# -*- coding:utf-8 -*-
class Solution:
    def __init__(self):
        self.q = []
        self.mi = []

    def push(self, node):
        min = self.min()
        if not self.mi or node <= min:
            self.mi.append(node)
        else:
            self.mi.append(min)
        self.q.append(node)

    def pop(self):
        if self.q:
            self.mi.pop()
            return self.q.pop()

    def top(self):
        if self.q:
            return self.q[-1]

    def min(self):
        if self.mi:
            return self.mi[-1]


s = Solution()
s.push(1)
s.push(2)
s.push(5)
s.push(3)
print(s.min())
print(s.pop())
print(s.top())