剑指offer32:从上到下打印二叉树

广度优先搜索

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

#方法1：用队列实现广度优先遍历
class Solution:
    def levelOrder(self,root):
        if not  root:
            return 
        queue=[]
        queue.append(root)
        res=[]
        while queue:
            curnode=queue.pop(0)#根节点入队
            res.append(curnode.value)
            if curnode.left:
                queue.append(curnode.left)
            if curnode.right:
                queue.append(curnode.right)
        return res

pNode1=TreeNode(8)
pNode2=TreeNode(6)
pNode3=TreeNode(10)
pNode4=TreeNode(5)
pNode5=TreeNode(7)
pNode6=TreeNode(9)
pNode7=TreeNode(11)

pNode1.left=pNode2
pNode1.right=pNode3
pNode2.left=pNode4
pNode2.right=pNode5
pNode3.left=pNode6
pNode3.right=pNode7
s=Solution()
s.levelOrder(pNode1)

#方法2：递归实现
def levelOrder_2(root):
    res=[]
    def helper(root,level):
        if not root:
            return None
        if len(res)==level:
            res.append([])
        res[level].append(root.value)
        helper(root.left,level+1)
        helper(root.right,level+1)
    helper(root,0)
    result=[]
    for i in res:
        result.extend(i)
    return result
s.levelOrder(pNode1)