Check if two strings have a common substring

You are given two strings str1 and str2. You have to check if the two strings share a common substring.

Examples :

Input : str1 = "HELLO"
        str2 = "WORLD"
Output : YES
Explanation :  The substrings "O" and
"L" are common to both str1 and str2

Input : str1 = "HI"
        str2 = "ALL"
Output : NO
Explanation : Because str1 and str2 
have no common substrings

A basic approach runs in O(n^2), where we compare every character of string 1 with every character of string 2 and replace every matched character with a “_” and set flag variable as true.



An efficient approach works in O(n). We basically need to check if there is a common character or not. We create a vector of size 26 for alphabets and initialize them as 0. For every character in string 1 we increment vector index of that character eg: v[s1[i]-‘a’]++, for every character of string 2 we check vector for the common characters if v[s2[i]-‘a’] > 0 then set flag = true and v[s2[i]-‘a’]– such that one character of string 2 is compared with only one character of string 1.

C++

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// CPP program to heck if two strings have
// common substring
#include <bits/stdc++.h>
using namespace std;
  
const int MAX_CHAR = 26;
  
// function to return true if strings have 
// common substring and no if strings have
// no common substring
bool twoStrings(string s1, string s2) {
  
  // vector for storing character occurrences
  vector<bool> v(MAX_CHAR, 0);
  
  // increment vector index for every
  // character of str1
  for (int i = 0; i < s1.length(); i++)
    v[s1[i] - 'a'] = true;
  
  // checking common substring of str2 in str1
  for (int i = 0; i < s2.length(); i++) 
    if (v[s2[i] - 'a']) 
       return true;
   
  return false;        
}
  
// driver program
int main() {
  string str1 = "hello";
  string str2 = "world";
  if (twoStrings(str1, str2))
     cout << "Yes";
  else
     cout << "No";
  return 0;
}

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Java

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// Java program to check if two strings have
// common substring
import java.util.Arrays;
  
class GFG
{
    static int MAX_CHAR = 26;
      
    // function to return true if strings have 
    // common substring and no if strings have
    // no common substring
    static boolean twoStrings(String s1, String s2) 
    {
        // vector for storing character occurrences
        boolean v[]=new boolean[MAX_CHAR];
        Arrays.fill(v,false);
      
        // increment vector index for every
        // character of str1
        for (int i = 0; i < s1.length(); i++)
            v[s1.charAt(i) - 'a'] = true;
          
        // checking common substring of str2 in str1
        for (int i = 0; i < s2.length(); i++) 
            if (v[s2.charAt(i) - 'a']) 
            return true;
          
        return false;     
    }
      
    // Driver code
    public static void main (String[] args) 
    {
        String str1 = "hello";
        String str2 = "world";
        if (twoStrings(str1, str2))
            System.out.print("Yes");
        else
            System.out.print("No");
    }
}
  
// This code is contributed by Anant Agarwal.

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Python 3

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# Python 3 program to heck if two 
# strings have common substring
MAX_CHAR = 26
  
# function to return true if 
# strings have common substring 
# and no if strings have no
# common substring
def twoStrings(s1, s2) :
  
    # vector for storing character
    # occurrences
    v = [0] * (MAX_CHAR)
      
    # increment vector index for every
    # character of str1
    for i in range(len(s1)):
        v[ord(s1[i]) - ord('a')] = True
      
    # checking common substring 
    # of str2 in str1
    for i in range(len(s2)) :
        if (v[ord(s2[i]) - ord('a')]) :
            return True
      
    return False
  
# Driver Code
if __name__ == "__main__":
    str1 = "hello"
    str2 = "world"
    if (twoStrings(str1, str2)):
        print("Yes")
    else:
        print("No")
  
# This code is contributed 
# by ChitraNayal

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C#

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// C# program to check if two 
// strings have common substring
using System;
  
class GFG
{
    static int MAX_CHAR = 26;
      
    // function to return true if strings have 
    // common substring and no if strings have
    // no common substring
    static bool twoStrings(String s1, String s2) 
    {
        // vector for storing character occurrences
        bool []v = new bool[MAX_CHAR];
          
    // Arrays.fill(v,false);
    for(int i = 0; i < MAX_CHAR; i++)
    v[i]=false;
      
        // increment vector index for 
        // every character of str1
        for (int i = 0; i < s1.Length; i++)
            v[s1[i] - 'a'] = true;
          
        // checking common substring of str2 in str1
        for (int i = 0; i < s2.Length; i++) 
            if (v[s2[i] - 'a']) 
            return true;
          
        return false;     
    }
      
    // Driver code
    public static void Main () 
    {
        String str1 = "hello";
        String str2 = "world";
        if (twoStrings(str1, str2))
            Console.Write("Yes");
        else
            Console.Write("No");
    }
}
  
// This code is contributed by nitin mittal.

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Output :

Yes

Time Complexity : O(n)



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Improved By : nitin mittal, chitranayal



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