Find Unique Binary String | Leetcode 1980

class Solution {
    string res;
    bool buildNumber(unordered_set<string>& numbers,string& curr,int& n){
        if(curr.size() == n){
            if(numbers.count(curr)==0){
                res = curr;
                return true;
            }
            return false;
        }
        //Try '0'
        curr.push_back('0');
        if(buildNumber(numbers,curr,n)) return true;
        curr.pop_back();

        //Try '1'
        curr.push_back('1');
        if(buildNumber(numbers,curr,n)) return true;
        curr.pop_back();

        return false;
    }
public:
    string findDifferentBinaryString(vector<string>& nums) {
        int n=nums.size();
        unordered_set<string> numbers(nums.begin(),nums.end());

        string curr="";
        buildNumber(numbers,curr,n);
        return res;
    }
};
/*
//JAVA
import java.util.*;

class Solution {
    private String res;

    private boolean buildNumber(Set<String> numbers, String curr, int n) {
        if (curr.length() == n) {
            if (!numbers.contains(curr)) {
                res = curr;
                return true;
            }
            return false;
        }

        // Try '0'
        if (buildNumber(numbers, curr + '0', n)) {
            return true;
        }

        // Try '1'
        if (buildNumber(numbers, curr + '1', n)) {
            return true;
        }

        return false;
    }

    public String findDifferentBinaryString(String[] nums) {
        int n = nums.length;
        Set<String> numbers = new HashSet<>(Arrays.asList(nums));
        buildNumber(numbers, "", n);
        return res;
    }
}

#Python
class Solution:
    def __init__(self):
        self.res = ""

    def buildNumber(self, numbers, curr, n):
        if len(curr) == n:
            if curr not in numbers:
                self.res = curr
                return True
            return False

        # Try '0'
        if self.buildNumber(numbers, curr + '0', n):
            return True

        # Try '1'
        if self.buildNumber(numbers, curr + '1', n):
            return True

        return False

    def findDifferentBinaryString(self, nums):
        n = len(nums)
        numbers = set(nums)
        self.buildNumber(numbers, "", n)
        return self.res

*/