Leetcode (5) 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.

简而言之，判断两棵二叉树是否相等，这里可以通过递归去判断，题目比较简单明了直接上代码吧。需要注意的是在判断左子树不相等的时候就可以直接return false了，而无需等左右子树都遍历完再返回结果。这样可以节省时间。运行时间为3 ms.

/**
 * 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) {
        if (!p && !q)
            return true;
        else if ( p && !q )
            return false;
        else if ( !p && q )
            return false;

        if (p->val != q->val)
            return false;
        else
        {
            if (!isSameTree(p->left, q->left))
                return false;
            if (!isSameTree(p->right, q->right))
                return false;
        }
        return true;
    }
};