LC 428. Serialize and Deserialize N-ary Tree

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/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Codec {
public:

    // Encodes a tree to a single string.
    string serialize(Node* root) {
        string res="";
        if(root==nullptr) return res;
        res+=to_string(root->val);
        res+=",";
        if(root->children.size()>0){
            dfs(res, root);
        }
        //cout<<res<<"
";
        return res;
    }

    void dfs(string &res, Node* root){
        res+="[,";
        for(auto &child:root->children){
            res+=to_string(child->val);
            res+=",";
            if(child->children.size()>0){
                dfs(res,child);
            }
        }
        res+="],";
    }

    // Decodes your encoded data to tree.
    Node* deserialize(string data) {
        if(data.size()==0) return nullptr;

        vector<string> parts=partString(data);
        //for(auto s:parts) cout<<s<<"
";
        Node* root=new Node(stoi(parts[0]));
        root->children=helper(parts,1,parts.size()-1);
        return root;
    }

    vector<Node*> helper(vector<string> &parts, int left, int right){
        vector<Node*> res;
        int lo=left+1;
        while(lo<right){
            Node* node=new Node(stoi(parts[lo]));
            if(lo+1<right && parts[lo+1]=="["){
                int cnt=1;
                int hi=lo+2;
                while(hi<right){
                    if(parts[hi]=="[") cnt++;
                    else if(parts[hi]=="]") cnt--;
                    if(cnt==0) break;
                    hi++;
                }
                node->children=helper(parts,lo+1,hi);
                lo=hi+1;
            }else{
                lo++;
            }
            res.push_back(node);
        }
        return res;
    }

    vector<string> partString(string data){
        int len=data.size();
        int start=0;
        int end=0;
        vector<string> res;
        while(start<len){
            while(data[end]!=',') end++;
            res.push_back(data.substr(start,end-start));
            start=end+1;
            end=start;
        }
        return res;
    }
};

// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));