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.

题意：判断两个树，形状和各个节点上的值是否完全相同。

java代码：

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