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【刷题】二叉树

时间:2021-01-14 11:27:23      阅读:0      评论:0      收藏:0      [点我收藏+]

标签:树的遍历   lse   while   pytho   ==   int   中序遍历   实战   turn   

树的构造

class TreeNode:
    def __init__(self,val,left=None,right=None):
        self.val=val
        self.left=left
        self.right=right
t7 = TreeNode(7)
t6 = TreeNode(6)
t5 = TreeNode(5)
t4 = TreeNode(4)
t3 = TreeNode(3,t6,t7)
t2 = TreeNode(2,t4,t5)
t1 = TreeNode(1,t2,t3)

二叉树的遍历

递归-先序遍历

res = []
def pre_order(root):
    global res
    if not root:
        return
    res.append(root.val)
    pre_order(root.left)
    pre_order(root.right)
pre_order(t1)
print("先序遍历:", res)

递归-中序遍历

res = []
def in_order(root):
    global res
    if not root:
        return
    in_order(root.left)
    res.append(root.val)
    in_order(root.right)
in_order(t1)
print("中序遍历:", res)

递归-后序遍历

res = []
def post_order(root):
    global res
    if not root:
        return
    post_order(root.left)
    post_order(root.right)
    res.append(root.val)
post_order(t1)
print("后序遍历:", res)

递归-层次遍历

def level_order(root):
    def helper(root, lev):
        if not root:
            return
        else:
            sol[lev-1].append(root.val)
            if len(sol) == lev:
                sol.append([])
            helper(root.left,lev + 1)
            helper(root.right, lev + 1)
    sol = [[]]
    helper(root, 1)
    return sol[:-1]
res = level_order(t1)
print("层次遍历:", res)

结果:
先序遍历: [1, 2, 4, 5, 3, 6, 7]
中序遍历: [4, 2, 5, 1, 6, 3, 7]
后序遍历: [4, 5, 2, 6, 7, 3, 1]
层次遍历: [[1], [2, 3], [4, 5, 6, 7]]

非递归-先序遍历

def pre_non_recursive_order(root):
    if not root:
        return []
    res = []
    stack = []
    while stack or root:
        while root:
            res.append(root.val)
            stack.append(root)
            root = root.left
        if stack:
            tmp = stack.pop()
            root = tmp.right
    return res
res = pre_non_recursive_order(t1)
print("先序遍历:", res)

非递归-中序遍历

def in_non_recursive_order(root):
    if not root:
        return []
    res = []
    stack = []
    while stack or root:
        while root:
            stack.append(root)
            root = root.left
        if stack:
            tmp = stack.pop()
            res.append(tmp.val)
            root = tmp.right
    return res
res = in_non_recursive_order(t1)
print("中序遍历:", res)

非递归-后序遍历

def post_non_recursive_order(root):
    if not root:
        return []
    res = []
    stack1 = [root]
    stack2 = []
    while stack1:
        tmp = stack1.pop()
        if tmp.left:
            stack1.append(tmp.left)
        if tmp.right:
            stack1.append(tmp.right)
        stack2.append(tmp)
    while stack2:
        res.append(stack2.pop().val)
    return res
res = post_non_recursive_order(t1)
print("后序遍历:", res)

非递归-层次遍历

def level_non_recursive_order(root):
    if not root:
        return  [[]]
    res = []
    queue = [root]
    while queue:
        tmp = []
        for i in range(len(queue)):
            t = queue.pop(0)
            tmp.append(t.val)
            if t.left:
                queue.append(t.left)
            if t.right:
                queue.append(t.right)
        res.append(tmp)
    return res
res = level_non_recursive_order(t1)
print("层次遍历:", res)

结果:
先序遍历: [1, 2, 4, 5, 3, 6, 7]
中序遍历: [4, 2, 5, 1, 6, 3, 7]
后序遍历: [4, 5, 2, 6, 7, 3, 1]
层次遍历: [[1], [2, 3], [4, 5, 6, 7]]

二叉树的序列化

(1)先序遍历
(2)后序遍历

二叉树的反序列化

(1)中序遍历
(2)后序遍历

实战

652 寻找重复的子树

未完待续。。。

【刷题】二叉树

标签:树的遍历   lse   while   pytho   ==   int   中序遍历   实战   turn   

原文地址:https://www.cnblogs.com/xiximayou/p/14269034.html

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