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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++

// 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; 
} 

Java

// 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. 

Python 3

# 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 

C#

// 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. 

Output :

Yes

Time Complexity : O(n)

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python 3

C#

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