leetcode(543). Diameter of Binary Tree
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problem
Given a binary tree, you need to compute the length of the diameter of
the tree. The diameter of a binary tree is the length of the longest
path between any two nodes in a tree. This path may or may not pass
through the root.
分析
这个问题就是找到一棵二叉树中两个节点之间最远的距离,其实也就是对任意的节点左右两棵子树深度的和的最大值,因此这里只要对求树的深度的代码做一点修改即可。
# Definition for a binary tree node.# class TreeNode(object):# def __init__(self, x):# self.val = x# self.left = None# self.right = Noneclass Solution(object): #self要定义在有self的地方 def diameterOfBinaryTree(self, root): """ :type root: TreeNode :rtype: int """ self.best = 0 def depth(r): if r == None: return 0 else: l = depth(r.left) r = depth(r.right) self.best = max(self.best, l+r) return 1 + max(l, r) depth(root) return self.best
总结
这个问题让我学会更加灵活的运用了递归算法,也就是利用递归算法的中间值,l = depth(r.left),r = depth(r.right), self.best = max(self.best, l+r)
,使用中间值修改全局变量进行记录,这样时间复杂度不变却增加了一个遍历的功能,获得每个节点的左右子树深度。
note:
这样的应用通常都是原问题与递归问题有一定联系,例如这里原问题是所有节点的左右子树深度和的最大值,递归问题是求树的深度,所以在递归中就会求到所有节点为根的树的深度,这样就将两个问题联系了起来。
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