jiang.py

class Solution(object):
    def diameterOfBinaryTree(self, root):
        if not root: return 0
        left = self.getHeight(root.left)
        right= self.getHeight(root.right)
        return max(left + right, max(self.diameterOfBinaryTree(root.left), self.diameterOfBinaryTree(root.right)))

    def getHeight(self, root):
        if not root: return 0
        left = self.getHeight(root.left)
        right = self.getHeight(root.right)
        return max(left, right) + 1