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void DFS(TreeNode* node,int &cnt){

    if(node->left==NULL && node->right==NULL)return;

    DFS(node->left,cnt);

    DFS(node->right,cnt);

    if(node->left && node->right){

        int leftdiff=abs(node->val-node->left->val);

        int rightdiff=abs(node->val-node->right->val);

        if(rightdiff==leftdiff){

            cnt++;

        }

    }

    return;

}

int countNodes(TreeNode* root){

    int cnt=0;

    DFS(root,cnt);

    return cnt;

}

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