Trie

/*
Practice:

Problem : https://codeforces.com/contest/842/problem/D 
Solution: https://codeforces.com/contest/842/submission/152356883 

Problem : https://codeforces.com/problemset/problem/282/E 
Solution: https://codeforces.com/contest/282/submission/152987420

Problem : https://codeforces.com/problemset/problem/633/C
Solution: https://codeforces.com/problemset/submission/633/276810614

/**/

// for distinct 26 characters. 

struct node{
    node *ch[26] ;
    bool isEnd;
    node()
    {
        isEnd = false;
        for(int i=0; i<26; i++)
        {
            ch[i] = NULL;
        }
    }
}*Root = new node();

void Insert(string s){
    node *curr=Root ;
    int i=0;
    for(char x:s)
    {
        i++;
        if(curr->ch[x-'a']==NULL)
        {
            curr->ch[x-'a']=new node() ;
        }
        curr=curr->ch[x-'a'];
        if(i==s.size())
        {
            curr->isEnd = true;
            break;
        }
    }
}

-----------------------------------

// for binary string 0/1.

struct node{
    node *ch[2] ;
    int cnt ;
    node()
    {
        ch[0]=ch[1]=NULL, cnt=0 ;
    }
}*root ;

void insert(int x){
    node *curr=root ;
    for(int i=20,bit; i>=0; --i){
        bit=(x>>i)&1 ;
        if(curr->ch[bit]==NULL)
            curr->ch[bit]=new node() ;
        curr=curr->ch[bit], curr->cnt++ ;
    }
}

int mex(int x){
    node *curr=root ; int num=0 ;
    for(int i=20,bit; i>=0; --i){
        bit=(x>>i)&1 ;
        if(curr->ch[bit]!=NULL and curr->ch[bit]->cnt==(1<<i))
            curr=curr->ch[bit^1] , num^=(1<<i) ;
        else
            curr=curr->ch[bit] ;
        if(curr==NULL)
            return num ;
    }
    return num ;
}