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Same Tree

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:

Input: 1 1 / \ / \ 2 3 2 3

    [1,2,3],   [1,2,3]

Output: true

Example 2:

Input: 1 1 / \ 2 2

    [1,2],     [1,null,2]

Output: false

Example 3:

Input: 1 1 / \ / \ 2 1 1 2

    [1,2,1],   [1,1,2]

Output: false

class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        }

        if (p == null || q == null) {
            return false;
        }

        if (p.val != q.val) { // !!!
            return false;
        }

        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}

Reference
https://leetcode-cn.com/problems/same-tree