LeetCode100 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.（Easy）

分析：

二叉树问题往往采用递归解决比较简单，这个题就是单纯的递归问题，以此判断两个根是否为空，节点值是否相等，左右孩子是否存在且递归判定相同。

/**
 * Definition for a binary tree node.
 * 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 == nullptr && q == nullptr) {
            return true;
        }
        else if (p == nullptr && q != nullptr) {
            return false;
        }
        else if (p != nullptr && q == nullptr) {
            return false;
        }
        else {
            if (p -> val != q -> val) {
                return false;
            }
            else {
                return (isSameTree(p -> left, q -> left) && isSameTree(p -> right, q -> right)) ;
            }
        }
    }
};