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Print all combinations generated by characters of a numeric string which does not exceed N
  • Last Updated : 08 Jan, 2021

Given a numeric string S of length M and an integer N, the task is to find all distinct combinations of S (repetitions allowed) that are at most N.

Examples:

Input: S = “124”, N = 100
Output: 1, 11, 12, 14, 2, 21, 22, 24, 4, 41, 42, 44
Explanation: Combinations “111”, “112”, “122”, “124”, “412” are greater than 100. Therefore, these combinations are excluded from the output.

Input: S = “345”, N = 400
Output: 3, 33, 333, 334, 335, 34, 343, 344, 345, 35, 353, 354, 355, 4, 43, 44, 45, 5, 53, 54, 55

Approach: The idea is to generate all the numbers possible using Backtracking and then print those numbers which does not exceed N. Follow the steps below to solve the problem:



  • Initialize a Set of strings, say combinations[], to store all distinct combinations of S that numerically does not exceed N.
  • Initialize a string ans to store the current combination of numbers possible from S.
  • Declare a function generateCombinations() to generate all required combinations whose values are less than the given value N and the function is defined as:
    • Traverse the string S over the range [0, M] using the variable i and do the following:
      • Push the current character S[i] to ans and convert the current string ans to the number and store it in x.
      • If x is less than or equal to N then push the string ans into combinations[] and recursively call the function generateCombinations().
    • Backtrack to its previous state by removing the ith character from ans.
  • After completing the above steps, print the set of all strings stored in combinations[].

Below is the implementation of the above approach:

C++




// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Store the current sequence of s
string combination;
 
// Store the all the required sequences
set<string> combinations;
 
// Function to print all sequences of S
// satisfying the required condition
void printSequences(
    set<string> combinations)
{
    // Print all strings in the set
    for (string s : combinations) {
        cout << s << ' ';
    }
}
 
// Function to generate all sequences
// of string S that are at most N
void generateCombinations(string& s, int n)
{
 
    // Iterate over string s
    for (int i = 0; i < s.size(); i++) {
 
        // Push ith character to combination
        combination.push_back(s[i]);
 
        // Convert the string to number
        long x = stol(combination);
 
        // Check if the condition is true
        if (x <= n) {
 
            // Push the current string to
            // the final set of sequences
            combinations.insert(combination);
 
            // Recursively call function
            generateCombinations(s, n);
        }
 
        // Backtrack to its previous state
        combination.pop_back();
    }
}
 
// Driver Code
int main()
{
    string S = "124";
    int N = 100;
 
    // Function Call
    generateCombinations(S, N);
 
    // Print required sequences
    printSequences(combinations);
 
    return 0;
}

Java




// Java program for the above approach
import java.util.*;
 
class GFG{
 
// Store the current sequence of s
static String combination = "";
 
// Store the all the required sequences
static HashSet<String> combinations = new LinkedHashSet<String>();
 
// Function to print all sequences of S
// satisfying the required condition
static void printSequences(
    HashSet<String> combinations)
{
     
    // Print all Strings in the set
    for(String s : combinations)
    {
        System.out.print(s + " ");
    }
}
 
// Function to generate all sequences
// of String S that are at most N
static void generateCombinations(String s, int n)
{
     
    // Iterate over String s
    for(int i = 0; i < s.length(); i++)
    {
         
        // Push ith character to combination
        combination += (s.charAt(i));
 
        // Convert the String to number
        long x = Integer.valueOf(combination);
 
        // Check if the condition is true
        if (x <= n)
        {
             
            // Push the current String to
            // the final set of sequences
            combinations.add(combination);
 
            // Recursively call function
            generateCombinations(s, n);
        }
 
        // Backtrack to its previous state
        combination = combination.substring(
            0, combination.length() - 1);
    }
}
 
// Driver Code
public static void main(String[] args)
{
    String S = "124";
    int N = 100;
     
    // Function Call
    generateCombinations(S, N);
 
    // Print required sequences
    printSequences(combinations);
}
}
 
// This code is contributed by Amit Katiyar

Python3




# Python3 program for the above approach
 
# Store the current sequence of s
combination = "";
 
# Store the all the required sequences
combinations = [];
 
# Function to print all sequences of S
# satisfying the required condition
def printSequences(combinations) :
     
    # Print all strings in the set
    for s in (combinations) :
        print(s, end = ' ');
  
# Function to generate all sequences
# of string S that are at most N
def generateCombinations(s, n) :   
    global combination;
 
    # Iterate over string s
    for i in range(len(s)) :
 
        # Push ith character to combination
        combination += s[i];
 
        # Convert the string to number
        x = int(combination);
 
        # Check if the condition is true
        if (x <= n) :
 
            # Push the current string to
            # the final set of sequences
            combinations.append(combination);
 
            # Recursively call function
            generateCombinations(s, n);
 
        # Backtrack to its previous state
        combination = combination[:-1];
 
# Driver Code
if __name__ == "__main__" :
 
    S = "124";
    N = 100;
 
    # Function Call
    generateCombinations(S, N);
 
    # Print required sequences
    printSequences(combinations);
 
    # This code is contributed by AnkThon

C#




// C# program for the above approach
using System;
using System.Collections.Generic;
class GFG
{
 
// Store the current sequence of s
static String combination = "";
 
// Store the all the required sequences
static SortedSet<String> combinations = new SortedSet<String>();
 
// Function to print all sequences of S
// satisfying the required condition
static void printSequences(
    SortedSet<String> combinations)
{
     
    // Print all Strings in the set
    foreach(String s in combinations)
    {
        Console.Write(s + " ");
    }
}
 
// Function to generate all sequences
// of String S that are at most N
static void generateCombinations(String s, int n)
{
     
    // Iterate over String s
    for(int i = 0; i < s.Length; i++)
    {
         
        // Push ith character to combination
        combination += (s[i]);
 
        // Convert the String to number
        long x = Int32.Parse(combination);
 
        // Check if the condition is true
        if (x <= n)
        {
             
            // Push the current String to
            // the readonly set of sequences
            combinations.Add(combination);
 
            // Recursively call function
            generateCombinations(s, n);
        }
 
        // Backtrack to its previous state
        combination = combination.Substring(
            0, combination.Length - 1);
    }
}
 
// Driver Code
public static void Main(String[] args)
{
    String S = "124";
    int N = 100;
     
    // Function Call
    generateCombinations(S, N);
 
    // Print required sequences
    printSequences(combinations);
}
}
 
// This code is contributed by 29AjayKumar
Output: 
1 11 12 14 2 21 22 24 4 41 42 44

 

Time Complexity: O(NN)
Auxiliary Space: O(NN)

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