Check if two strings have a common substring

Last Updated : 27 Jan, 2023

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.

Implementation:

C++

// CPP program to check 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.

Python3

# Python3 code to implement the approach  # python program to check 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 for i in range(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 program str1 = "hello" str2 = "world" if twoStrings(str1, str2):     print("Yes") else:     print("No")  # This code is contributed by phasing17

// 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.

JavaScript

<script>  // javascript program to check if two strings have // common substring  var MAX_CHAR = 26;  // function to return true if strings have  // common substring and no if strings have // no common substring function twoStrings(s1, s2) {    // vector for storing character occurrences   var v = Array(MAX_CHAR).fill(0);    // increment vector index for every   // character of str1   for (var i = 0; i < s1.length; i++)     v[s1[i] - 'a'] = true;    // checking common substring of str2 in str1   for (var i = 0; i < s2.length; i++)      if (v[s2[i] - 'a'])         return true;     return false;         }  // driver program var str1 = "hello"; var str2 = "world"; if (twoStrings(str1, str2))    document.write( "Yes"); else    document.write("No");  // This code is contributed by rutvik_56. </script>

Output

Yes

Time Complexity : O(n)
Auxiliary Space: O(1)

Check if there is any common character in two given strings

Shivam.Pradhan

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Check if two strings have a common substring

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