递归计数子字符串的出现

给定两个字符串str1和str2，任务是使用递归计算“ str1”在“ str1”中出现的次数。

例子：

Input : str1 = "geeksforgeeks", str2 = "geek"
Output : 2

Input: kanekihiishishi
Output: 3

假设问题有n个部分，以考虑已经完成的n-1个部分的方式划分问题，然后将要执行的操作限制为仅一个部分。从而，将递归方法分为两种情况，即基本情况和递归情况。
在此特定问题中，基本情况涉及以下事实：如果str1的长度小于str2的长度。

现在，在讨论递归情况时，将str1的第一个子字符串与str2进行比较，然后对剩余的str1进行递归。

C++

// Recursive C++ program for counting number of substrings
#include 
#include 
using namespace std;
  
// Recursive function to count
// the number of occurrences of "hi" in str.
int countSubstrig(string str1, string str2)
{
    int n1 = str1.length();
    int n2 = str2.length();
  
    // Base Case
    if (n1 == 0 || n1 < n2)
        return 0;
  
    // Recursive Case
    // Checking if the first substring matches
    if (str1.substr(0, n2).compare(str2) == 0)
        return countSubstrig(str1.substr(n2-1), str2) + 1;
  
    // Otherwise, return the count from
    // the remaining index
    return countSubstrig(str1.substr(n2-1), str2);
}
  
// Driver function
int main()
{
    string str1 = "geeksforgeeks", str2 = "geeks";
    cout << countSubstrig(str1, str2) << endl;
  
    str1 = "hikakashi", str2 = "hi";
    cout << countSubstrig(str1, str2) << endl;
    return 0;
}

Java

// Recursive Java program for
// counting number of substrings
class GFG
{
  
// Recursive function to 
// count the number of 
// occurrences of "hi" in str.
static int countSubstrig(String str1, 
                         String str2)
{
    int n1 = str1.length();
    int n2 = str2.length();
  
    // Base Case
    if (n1 == 0 || n1 < n2)
        return 0;
  
    // Recursive Case
    // Checking if the first
    // substring matches
    if (str1.substring(0, n2).equals(str2))
        return countSubstrig(str1.substring(n2 - 1), 
                                            str2) + 1;
  
    // Otherwise, return the count 
    // from the remaining index
    return countSubstrig(str1.substring(n2 - 1), 
                                        str2);
}
  
// Driver Code
public static void main(String args[])
{
    String str1 = "geeksforgeeks", 
           str2 = "geeks";
    System.out.println(countSubstrig(str1, 
                                     str2));
  
    str1 = "hikakashi";
    str2 = "hi";
    System.out.println(countSubstrig(str1, 
                                     str2));
  
}
}
  
// This code is contributed 
// by Arnab Kundu

Python3

# Recursive Python3 program for
# counting number of substrings
  
# Recursive function to 
# count the number of 
# occurrences of "hi" in str.
def countSubstrig(str1, str2):
      
    n1 = len(str1);
    n2 = len(str2);
      
    # Base Case
    if (n1 == 0 or n1 < n2):
        return 0;
  
    # Recursive Case
    # Checking if the first
    # substring matches
    if (str1[0 : n2] == str2):
        return countSubstrig(str1[n2 - 1:], 
                             str2) + 1;
  
    # Otherwise, return the count 
    # from the remaining index
    return countSubstrig(str1[n2 - 1:], 
                         str2);
  
# Driver Code
if __name__ == '__main__':
      
    str1 = "geeksforgeeks"; 
    str2 = "geeks";
    print(countSubstrig(str1, str2));
  
    str1 = "hikakashi";
    str2 = "hi";
    print(countSubstrig(str1, str2));
  
# This code is contributed by Princi Singh

C#

// Recursive C# program for
// counting number of substrings
using System;
class GFG
{
  
// Recursive function to 
// count the number of 
// occurrences of "hi" in str.
static int countSubstrig(String str1, 
                         String str2)
{
    int n1 = str1.Length;
    int n2 = str2.Length;
  
    // Base Case
    if (n1 == 0 || n1 < n2)
        return 0;
  
    // Recursive Case
    // Checking if the first
    // substring matches
    if (str1.Substring(0, n2).Equals(str2))
        return countSubstrig(str1.Substring(n2 - 1), 
                                            str2) + 1;
  
    // Otherwise, return the 
    // count from the remaining 
    // index
    return countSubstrig(str1.Substring(n2 - 1), 
                                        str2);
}
  
// Driver Code
public static void Main()
{
    string str1 = "geeksforgeeks", 
           str2 = "geeks";
    Console.Write(countSubstrig(str1, 
                                str2));
    Console.Write("\n");
      
    str1 = "hikakashi";
    str2 = "hi";
    Console.Write(countSubstrig(str1, 
                                str2));
  
}
}
  
// This code is contributed 
// by Smita

输出：

2
2