Given a string of lowercase English alphabets. The task is to check if there exists any subsequence in the string which is not a palindrome. If there is at least 1 subsequence which is not a palindrome then print YES, otherwise print NO.
Examples:
Input : str = "abaab" Output : YES Subsequences "ab" or "abaa" or "aab", are not palindrome. Input : str = "zzzz" Output : NO All possible subsequences are palindrome.
The main observation is that if the string contains at least two distinct characters, then there will always be a subsequence of length at least two which is not a palindrome. Only if all the characters of the string are same then there will not be any subsequence which is not a palindrome. Because in an optimal way we can choose any two distinct characters from a string and place them in same order one after each to form a non-palindromic string.
Below is the implementation of above approach:
C++
// C++ program to check if there exists // at least 1 sub-sequence in a string // which is not palindrome #include <bits/stdc++.h> using namespace std; // Function to check if there exists // at least 1 sub-sequence in a string // which is not palindrome bool isAnyNotPalindrome(string s) { // use set to count number of // distinct characters set<char> unique; // insert each character in set for (int i = 0; i < s.length(); i++) unique.insert(s[i]); // If there is more than 1 unique // characters, return true if (unique.size() > 1) return true; // Else, return false else return false; } // Driver code int main() { string s = "aaaaab"; if (isAnyNotPalindrome(s)) cout << "YES"; else cout << "NO"; return 0; } |
Java
// Java program to check if there exists // at least 1 sub-sequence in a string // which is not palindrome import java.util.*; class GFG { // Function to check if there exists // at least 1 sub-sequence in a string // which is not palindrome static boolean isAnyNotPalindrome(String s) { // use set to count number of // distinct characters Set<Character> unique=new HashSet<Character>(); // insert each character in set for (int i = 0; i < s.length(); i++) unique.add(s.charAt(i)); // If there is more than 1 unique // characters, return true if (unique.size() > 1) return true; // Else, return false else return false; } // Driver code public static void main(String []args) { String s = "aaaaab"; if (isAnyNotPalindrome(s)) System.out.println("YES"); else System.out.println("NO"); } } |
Python3
# Python3 program to check if there exists # at least 1 sub-sequence in a string # which is not palindrome # Function to check if there exists # at least 1 sub-sequence in a string # which is not palindrome def isAnyNotPalindrome(s): # use set to count number of # distinct characters unique=set() # insert each character in set for i in range(0,len(s)): unique.add(s[i]) # If there is more than 1 unique # characters, return true if (len(unique) > 1): return True # Else, return false else: return False # Driver code if __name__=='__main__': s = "aaaaab" if (isAnyNotPalindrome(s)): print("YES") else: print("NO") # This code is contributed by # ihritik |
C#
// C# program to check if there exists // at least 1 sub-sequence in a string // which is not palindrome using System; using System.Collections.Generic; class GFG { // Function to check if there exists // at least 1 sub-sequence in a string // which is not palindrome static bool isAnyNotPalindrome(String s) { // use set to count number of // distinct characters HashSet<char> unique=new HashSet<char>(); // insert each character in set for (int i = 0; i < s.Length; i++) unique.Add(s[i]); // If there is more than 1 unique // characters, return true if (unique.Count > 1) return true; // Else, return false else return false; } // Driver code public static void Main(String []args) { String s = "aaaaab"; if (isAnyNotPalindrome(s)) Console.WriteLine("YES"); else Console.WriteLine("NO"); } } // This code contributed by Rajput-Ji |
YES
Time Complexity: O(N), where N is the length of the string.
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