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Same Tree 

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.

分析

题意是：给定2颗二叉树，写一个检查这两颗二叉树是否相等的函数

对树的问题，递归总是一种思路。对于这个判断二叉树相等的问题，我们可以想象一下，如果两颗二叉树果真相等，那么他们的每个节点的val值肯定相等的，他们的左子树和右子树也肯定是相等的。而判断他们左子树和右子树是否相等，是一个递归子问题。

Code

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode *p, TreeNode *q) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if( !p && !q)
            return true;
        if( !p || !q)
            return false;
        if( p->val != q->val)
            return false;
        if( isSameTree(p->left, q->left) == false)
            return false;
        if( isSameTree(p->right, q->right) == false)
            return false;
        return true;
    }
};

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