打印由不超过 N 的数字字符串的字符生成的所有组合

给定长度为M的数字字符串S和整数N ，任务是找到S 的所有不同组合(允许重复)，最多为N 。

例子：

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

方法：这个想法是使用回溯生成所有可能的数字，然后打印那些不超过N 的数字。请按照以下步骤解决问题：

• 初始化一组字符串，比如组合[]，以存储S 的所有不同组合，这些组合在数字上不超过N 。
• 初始化字符串ans以存储S 中可能的当前数字组合。
• 声明一个函数generateCombinations()以生成其值小于给定值N 的所有必需组合，该函数定义为：
  • 使用变量i在[0, M]范围内遍历字符串S并执行以下操作：
    • 将当前字符S[i]推送到ans并将当前字符串ans转换为数字并存储在x 中。
    • 如果x小于或等于N，则将字符串ans推入组合 []并递归调用函数generateCombinations() 。
  • 通过从ans 中删除第i^个字符来回溯到其先前的状态。
• 完成上述步骤后，打印存储在组合[]中的所有字符串的集合。

下面是上述方法的实现：

C++

// C++ program for the above approach
#include 
using namespace std;
 
// Store the current sequence of s
string combination;
 
// Store the all the required sequences
set combinations;
 
// Function to print all sequences of S
// satisfying the required condition
void printSequences(
    set 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 combinations = new LinkedHashSet();
 
// Function to print all sequences of S
// satisfying the required condition
static void printSequences(
    HashSet 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 combinations = new SortedSet();
 
// Function to print all sequences of S
// satisfying the required condition
static void printSequences(
    SortedSet 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

Javascript

      // JavaScript program for the above approach
      // Store the current sequence of s
      var combination = "";
 
      // Store the all the required sequences
      var combinations = [];
 
      // Function to print all sequences of S
      // satisfying the required condition
      function printSequences(combinations) {
        // Print all Strings in the set
        for (var s of combinations) {
          document.write(s + " ");
        }
      }
 
      // Function to generate all sequences
      // of String S that are at most N
      function generateCombinations(s, n) {
        // Iterate over String s
        for (var i = 0; i < s.length; i++) {
          // Push ith character to combination
          combination += s[i];
 
          // Convert the String to number
          var x = parseInt(combination);
 
          // Check if the condition is true
          if (x <= n) {
            // Push the current String to
            // the readonly set of sequences
            combinations.push(combination);
 
            // Recursively call function
            generateCombinations(s, n);
          }
 
          // Backtrack to its previous state
          combination = combination.substring(0, combination.length - 1);
        }
      }
 
      // Driver Code
      var S = "124";
      var N = 100;
 
      // Function Call
      generateCombinations(S, N);
 
      // Print required sequences
      printSequences(combinations);
    

输出：

1 11 12 14 2 21 22 24 4 41 42 44

时间复杂度： O(N ^N )
辅助空间： O(N ^N )

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