二叉樹遍歷與遞歸及非遞歸實現方法

二叉樹的遍歷真的是編了忘忘了編，直接Mark到這邊以便查閱。

樹的相關知識：👉

堆的相關知識：👉數據結構：堆(Heap)

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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深度優先

前序遍歷：先根再左後右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)

 輸出：[10, 6, 4, 8, 13, 0, 1, 16] 

中序遍歷：先左再根後右 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: 壓中左，彈左，再壓右

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

 中序的非遞歸算法和可以當作回溯法在二叉樹上搜索的應用。

即若節點不存在，則尋找上一級節點。解空間就是樹的val組成的空間，因此沒有限制條件。

 輸出： [4, 6, 8, 10, 1, 0, 13, 16]

後續遍歷：先左再右後根 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正常彈中壓左右，彈去STACKSAVE，最後STACKSAVE彈出 

def DSFbyStackLRD(root):
    if root is not None:
        stack = []
        stack.append(root)
        stackSave = []
        #多用一個stackSave來承載
        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)

 輸出：[4, 8, 6, 1, 0, 16, 13, 10]

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廣度優先

使用隊列：前出中壓左右