# 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 ` `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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Improved By : nitin mittal, chitranayal

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