Cracking The Coding Interview 4.7_暂存

//原文：
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//	You have two very large binary trees: T1, with millions of nodes, and T2, with hundreds of nodes. Create an algorithm to decide if T2 is a subtree of T1
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//	译文：
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//	有两棵很大的二叉树：T1有上百万个结点，T2有上百个结点。写程序判断T2是否为T1的子树。

除了暴力法，没想到更好的。。暂时放这