二叉树遍历与递归及非递归实现方法

二叉树的遍历真的是编了忘忘了编，直接Mark到这边以便查阅。

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

a = TreeNode(10)
a.left = TreeNode(6)
a.right = TreeNode(13)
a.left.left = TreeNode(4)
a.left.right = TreeNode(8)
a.right.left = TreeNode(0)
a.right.right = TreeNode(16)
a.right.left.left = TreeNode(1)

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深度优先

前序遍历：先根再左后右DLR

def DSFbyRecurrentDLR(ListPrint,root): #(root)
    if root is not None:
        #print(root.val)
        ListPrint.append(root.val)
        if root.left is not None:
            DSFbyRecurrentDLR(ListPrint, root.left)
            pass
        if root.right is not None:
            DSFbyRecurrentDLR(ListPrint, root.right)
            pass

def testDSFbyRecurrentDLR(root):
    k = []
    DSFbyRecurrentDLR(k, root)
    print(k)

testDSFbyRecurrentDLR(a)

def DSFbyStackDLR(root):
    if root is not None:
        stack = []
        stack.append(root)
        while len(stack) :
            cur_node = stack.pop()
            print(cur_node.val)
            if cur_node.right is not None:
                stack.append(cur_node.right)
            if cur_node.left is not None:
                stack.append(cur_node.left)

DSFbyStackDLR(a)

 输出：[10, 6, 4, 8, 13, 0, 1, 16] 

中序遍历：先左再根后右 LDR 

def DSFbyRecurrentLDR(ListPrint, root): #(root)
    if root is not None:
        if root.left is not None:
            DSFbyRecurrentLDR(ListPrint, root.left)
            pass
        #print(root.val)
        ListPrint.append(root.val)
        if root.right is not None:
            DSFbyRecurrentLDR(ListPrint, root.right)
            pass

def testDSFbyRecurrentLDR(root):
    k = []
    DSFbyRecurrentLDR(k, root)
    print(k)

testDSFbyRecurrentLDR(a)

Warning: 压中左，弹中，再压右

def DSFbyStackLDR(root):
    if root is not None:
        # if the memory path is needed, a stack must be needed
        stack = []
        cur = root  # the scanning cur_p for rootTree
        while len(stack) or cur is not None:
            while cur is not None:
                stack.append(cur)
                cur = cur.left

            cur = stack.pop()
            print(cur.val)
            cur = cur.right

 输出： [4, 6, 8, 10, 1, 0, 13, 16]

后续遍历：先左再右后根 LRD

def DSFbyRecurrentLRD(ListPrint, root): #(root)
    if root is not None:
        if root.left is not None:
            ListPrint.append(DSFbyRecurrentLRD(ListPrint, root.left))
            #DSFbyRecurrent(root.left)
            pass
        if root.right is not None:
            ListPrint.append(DSFbyRecurrentLRD(ListPrint, root.right))
            # DSFbyRecurrent(root.right)
        #print(root.val)
        return root.val

def testDSFbyRecurrentLRD(root):
    k = []
    k.append(DSFbyRecurrentLRD(k, root))
    print(k)

testDSFbyRecurrentLRD(a)

Warning: STACK正常弹中压左右，弹去STACKSAVE，最后STACKSAVE弹出 

def DSFbyStackLRD(root):
    if root is not None:
        stack = []
        stack.append(root)
        stackSave = []
        #多用一个stackSave来承载
        while len(stack):
            cur_node = stack.pop()
            stackSave.append(cur_node)
            if cur_node.left is not None:
                stack.append(cur_node.left)
            if cur_node.right is not None:
                stack.append(cur_node.right)

        # print(stack)

        while len(stackSave):
            k = stackSave.pop().val
            print(k)

# DSFbyStackDLR(a)
DSFbyStackLRD(a)

 输出：[4, 8, 6, 1, 0, 16, 13, 10]

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广度优先

使用队列：前出中压左右