# Check if two same sub-sequences exist in a string or not

Given a string, the task is to check if there exist two equal sub-sequences in the given string. Two sub-sequences are said to be equal if they have the same characters arranged in the same lexicographical order but the position of characters differs from that in the original string.

**Examples:**

Input:str = “geeksforgeeks”

Output:YES

Two possible sub-sequences are “geeks” and “geeks”.

Input:str = “bhuvan”

Output:NO

**Approach:** The approach to solve this problem is to check if any character appears more than once. Since the minimal length of matching subsequence can be 1, hence if a character occurrence in a string more than once then two similar subsequences is possible. Initialize a *freq[]* array of length 26. Iterate over the string and increment the characters frequency. Iterate over the freq array and check if freq[i] for any i in range of 0-26 is more than 1, then it is possible.

Below is the implementation of the above approach.

## C++

`// C++ program to Check if ` `// similar subsequences exist or not ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Function to check if similar subsequences ` `// occur in a string or not ` `bool` `check(string s, ` `int` `l) ` `{ ` ` ` ` ` `int` `freq[26] = { 0 }; ` ` ` `// iterate and count the frequency ` ` ` `for` `(` `int` `i = 0; i < l; i++) { ` ` ` `freq[s[i] - ` `'a'` `]++; ` `// counting frequency of the letters ` ` ` `} ` ` ` ` ` `// check if frequency is more ` ` ` `// than once of any character ` ` ` `for` `(` `int` `i = 0; i < 26; i++) { ` ` ` `if` `(freq[i] >= 2) ` ` ` `return` `true` `; ` ` ` `} ` ` ` `return` `false` `; ` `} ` `// Driver Code ` `int` `main() ` `{ ` ` ` `string s = ` `"geeksforgeeks"` `; ` ` ` `int` `l = s.length(); ` ` ` `if` `(check(s, l)) ` ` ` `cout << ` `"YES"` `; ` ` ` `else` ` ` `cout << ` `"NO"` `; ` ` ` ` ` `return` `0; ` `} ` |

*chevron_right*

*filter_none*

## Java

`// Java program to Check ` `// if similar subsequences ` `// exist or not ` `import` `java.io.*; ` `import` `java.util.*; ` `import` `java.util.Arrays; ` ` ` `class` `GFG ` `{ ` `// Function to check if ` `// similar subsequences ` `// occur in a string or not ` `static` `boolean` `check(String s, ` ` ` `int` `l) ` `{ ` ` ` `int` `freq[] = ` `new` `int` `[` `26` `]; ` ` ` `Arrays.fill(freq, ` `0` `); ` ` ` ` ` `// iterate and count ` ` ` `// the frequency ` ` ` `for` `(` `int` `i = ` `0` `; i < l; i++) ` ` ` `{ ` ` ` `// counting frequency ` ` ` `// of the letters ` ` ` `freq[s.charAt(i) - ` `'a'` `]++; ` ` ` `} ` ` ` ` ` `// check if frequency is more ` ` ` `// than once of any character ` ` ` `for` `(` `int` `i = ` `0` `; i < ` `26` `; i++) ` ` ` `{ ` ` ` `if` `(freq[i] >= ` `2` `) ` ` ` `return` `true` `; ` ` ` `} ` ` ` `return` `false` `; ` `} ` ` ` `// Driver Code ` `public` `static` `void` `main(String args[]) ` `{ ` ` ` `String s = ` `"geeksforgeeks"` `; ` ` ` `int` `l = s.length(); ` ` ` `if` `(check(s, l)) ` ` ` `System.out.print(` `"YES"` `); ` ` ` `else` ` ` `System.out.print(` `"NO"` `); ` `} ` `} ` |

*chevron_right*

*filter_none*

## Python3

# Python 3 program to Check if

# similar subsequences exist or not

# Function to check if similar subsequences

# occur in a string or not

def check(s, l):

freq = [0 for i in range(26)]

# iterate and count the frequency

for i in range(l):

# counting frequency of the letters

freq[ord(s[i]) – ord(‘a’)] += 1

# check if frequency is more

# than once of any character

for i in range(26):

if (freq[i] >= 2):

return True

return False

# Driver Code

if __name__ == ‘__main__’:

s = “geeksforgeeks”

l = len(s)

if (check(s, l)):

print(“YES”)

else:

print(“NO”)

# This code is contributed by

# Sahil_Shelangia

**Output:**

YES

**Time Complexity:** O(N)

**Auxiliary Space:** O(1)

**Note**: If the length of similar subsequence was mentioned, then the approach to solve the problem will also be different. The approach to check if a string contains two repeated subsequences of length two or more is discussed in this post.

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