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class Solution {
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 public:
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  bool isSameTree(TreeNode *p, TreeNode *q) {
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    if (p == NULL || q == NULL) return q == p;
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    if (p->val != q->val) return false;
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    return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
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  }
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};