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Problem Definition:
Given a binary tree, determine if it is height-balanced.
For this problem, a height-balanced binary tree is defined as a
binary tree in which the depth of the two subtrees of every node never differ by more than 1.
这里面临的问题是，既要记录子树的高度，又要记录子树是否平衡。
Solution 1: 只记录子树是否平衡，每次都重新计算高度，太耗时。
Solution 2: 用一个tuple来记录高度和平衡。
1 # @param {TreeNode} root 2 # @return {boolean} 3 def isBalanced(root): 4 b,h=func(root) 5 return b 6 7 def func(root): 8 if root==None: 9 return (True,0) 10 lb,lh=func(root.left) 11 rb,rh=func(root.right) 12 return (abs(lh-rh)<=1 and lb and rb, max(lh,rh)+1) 13
Solution 3: 把这两个变量结合在一起，用一个负数表示不平衡时的高度。
1 def isBalanced(self, root): 2 return self.height(root)!=-1 3 4 def height(self,root): 5 if root==None: 6 return 0 7 hl=self.height(root.left) 8 hr=self.height(root.right) 9 if hl==-1 or hr==-1 or abs(hl-hr)>1: 10 return -1 11 return max(hl,hr)+1
LeetCode#110 Balanced Binary Tree
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原文地址：http://www.cnblogs.com/acetseng/p/4665703.html
