1.二叉樹的層次遍歷 遞迴解法

class Node(object):
    def __init__(self, v, left=None, right=None):
        self.value = v
        self.left = left
        self.right = right

# 層次遍歷入口函式
def level_tranverse_iterate(node):
    if not node:
        return 0
    depth = Depth(node)
    print "depth:", depth
    for i in
 
 range(1, depth+1):
        print_node_at_level(node, i)
        print 

# 計算樹高
def Depth(node):
    if not node:
        return 0
    return max(Depth(node.left)+1,Depth(node.right)+1)

# 當level=1時才輸出結點
def print_node_at_level(node, level):
    if not node or level < 1:
        return 0
    if level == 1
 
:
        print node.value,
        return 0
    print_node_at_level(node.left, level-1)
    print_node_at_level(node.right, level-1)


node = Node(1, Node(3, Node(7, Node(0)), Node(6)), Node(2, Node(5), Node(4)))
level_tranverse_iterate(node)
# output:
depth: 4
1
3 2
7 6 5 4
0

2.非遞迴解法

def level_tranverse_noniterate
 
(node):
    stack = [node]
    while stack:
        node = stack.pop(0)
        print node.value
        if node.left:
            stack.append(node.left)
        if node.right:
            stack.append(node.right)


node = Node(1, Node(3, Node(7, Node(0)), Node(6)), Node(2, Node(5), Node(4)))

level_tranverse_noniterate(node)
output:
1 3 2 7 6 5 4 0

3.從底向上的層次遍歷 非遞迴解法

就是將樹
1
3 2
7 6 5 4
0
列印為:
0   7 6 5 4    3 2     1

主要是要考慮每層的元素要分隔開，不然會亂。

# python 2.7
def from_bottom_to_top(node):
    if not node:
        return 0

    vect = [node]
    cur = 0
    last = 1

    while cur < len(vect):
        vect.append(None)   # 以None作為層之間的分隔
        last = len(vect)
        print "每層個數"+str(last-cur)
        # 每層的結點都判斷是否有左右子結點
        # 用cur來計數，cur==last-1即當前層的結點全部判斷完了
        #然後cur += 1，如果cur==len(vect)，說明下一層沒有新結點加入，層次遍歷結束
        while cur < last - 1:
            if vect[cur].right:
                vect.append(vect[cur].right)
            if vect[cur].left:
                vect.append(vect[cur].left)
            cur += 1 
        cur+= 1

    # 按層輸出
    for i in range(len(vect)):
        if vect[i]:
            print vect[i].value,
        else:
            print