What is wrong with this recursive solution (time limit exceed)?

  • 0
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node ==NULL) return node;
        UndirectedGraphNode* head = new UndirectedGraphNode(node -> label); 
        for (auto x : node -> neighbors) {
            if (x->label != head->label)
        return head;

    I think most solutions use unordered_map and check if the node has been visited (it connects to itself) by checking if the node is already in the unordered map. I am just confused why this is different from "x->label != head->label"? Or there may be other problems with this implementation. Thanks for your help!

  • 0

    "x->label != head->label" is not enough for detecting a loop that has 3 and more nodes. You will enter an infinite loop in such situation.

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