Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
递归：如果root均为null则全等，如果root非null，则子树全等＋root值相同=>两树全等。
def is_same_tree(p, q) return true if not p and not q return is_same_tree(p.left,q.left) && is_same_tree(p.right,q.right) if p and q and p.val == q.val false end
循环：expected to be added...
原文：http://www.cnblogs.com/lilixu/p/4589598.html