Ya did the same thing... have a look at my piece of code

int maxSubsequenceLength(int n,int k,vector<int>arr){
	int maxe=*max_element(arr.begin(),arr.end());
	vector<int>all_pos[maxe+1];
	for(int i=0;i<n;i++)
		all_pos[arr[i]].pb(i);
	vector<bool>vis(n+1,false);
	unordered_map<int,bool>hash;
	for(int i=0;i<n;i++)
		hash[arr[i]]=true;
	int ans=1;
	for(int i=0;i<n;i++){
		if(hash[k^arr[i]]==true and vis[i]==false){
			int a=arr[i];
			int b=k^arr[i];
			int count=1;
			bool first=false;
			int pos=i;
			vis[pos]=true;
			while(1){
				if(first){
					auto it=upper_bound(all_pos[a].begin(),all_pos[a].end(),pos);
					if(it==all_pos[a].end()){
						break;
					}
					count++;
					pos=all_pos[a][it-all_pos[a].begin()];
					vis[pos]=true;
					first=false;
				}
				else{
					auto it=upper_bound(all_pos[b].begin(),all_pos[b].end(),pos);
					if(it==all_pos[b].end()){
						break;
					}
					count++;
					pos=all_pos[b][it-all_pos[b].begin()];
					vis[pos]=true;
					first=true;
				}
			}
			ans=max(ans,count);
		}
	}
	return ans;
}