Check if given string is a substring of string formed by repeated concatenation of z to a
Last Updated :
15 Jul, 2025
Given a string str, the task is to check if string str is a substring of an infinite length string S in which lowercase alphabets are concatenated in reverse order as:
S = "zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba...."
Examples:
Input: str = "cbaz"
Output: YES
Explanation:
Given string "cbaz" is a valid sub string of S.
Input: str = "ywxtuv"
Output: NO
Explanation:
Given string "ywxtuv" is a valid sub string of S.
Approach: It can be observed that every next character has a lower ASCII value than the previous character except when 'a' is followed by 'z'. The best way to solve this problem is to simply check for every character if the character following it has a lower ASCII value. Ignore this comparison when the current character is 'a'. If the current character 'a' occurred then check if it is followed by character is 'z'.
Below are the steps:
- Create a flag variable to mark if a given string is a valid substring or not. Initially set it to true.
- Traverse the given string str, and for every character, str[i] do the following:
- If str[i+1] + 1 < str[i], continue with the loop.
- If str[i] = 'a' and str[i+1] = 'z', again continue with the loop.
- Else mark flag variable as false and break from the loop.
- Finally, if the flag is true print YES else print NO.
Below is the implementation of the above approach :
C++
// C++ program for the above approach
#include <iostream>
using namespace std;
// Function checks if a given string is
// valid or not and prints the output
void checkInfinite(string s)
{
// Boolean flag variable to mark
// if given string is valid
bool flag = 1;
int N = s.length();
// Traverse the given string
for (int i = 0; i < N - 1; i++) {
// If adjacent character
// differ by 1
if (s[i] == char(int(s[i + 1]) + 1)) {
continue;
}
// If character 'a' is
// followed by 4
else if (s[i] == 'a'
&& s[i + 1] == 'z') {
continue;
}
// Else flip the flag and
// break from the loop
else {
flag = 0;
break;
}
}
// Output according to flag variable
if (flag == 0)
cout << "NO";
else
cout << "YES";
}
// Driver Code
int main()
{
// Given string
string s = "ecbaz";
// Function Call
checkInfinite(s);
return 0;
}
// Java program for the above approach
class GFG{
// Function checks if a given string is
// valid or not and prints the output
public static void checkInfinite(String s)
{
// Boolean flag variable to mark
// if given string is valid
boolean flag = true;
int N = s.length();
// Traverse the given string
for(int i = 0; i < N - 1; i++)
{
// If adjacent character
// differ by 1
if (s.charAt(i) == (char)((int)
(s.charAt(i + 1)) + 1))
{
continue;
}
// If character 'a' is
// followed by 4
else if (s.charAt(i) == 'a' &&
s.charAt(i + 1) == 'z')
{
continue;
}
// Else flip the flag and
// break from the loop
else
{
flag = false;
break;
}
}
// Output according to flag variable
if (!flag)
System.out.print("NO");
else
System.out.print("YES");
}
// Driver code
public static void main(String[] args)
{
// Given string
String s = "ecbaz";
// Function call
checkInfinite(s);
}
}
// This code is contributed by divyeshrabadiya07
# Python3 program for the above approach
# Function checks if a given is
# valid or not and prints the output
def checkInfinite(s):
# Boolean flag variable to mark
# if given is valid
flag = 1
N = len(s)
# Traverse the given string
for i in range(N - 1):
# If adjacent character
# differ by 1
if (s[i] == chr(ord(s[i + 1]) + 1)):
continue
# If character 'a' is
# followed by 4
elif (s[i] == 'a' and s[i + 1] == 'z'):
continue
# Else flip the flag and
# break from the loop
else:
flag = 0
break
# Output according to flag variable
if (flag == 0):
print("NO")
else:
print("YES")
# Driver Code
if __name__ == '__main__':
# Given string
s = "ecbaz"
# Function Call
checkInfinite(s)
# This code is contributed by mohit kumar 29
// C# program for the above approach
using System;
class GFG{
// Function checks if a given string is
// valid or not and prints the output
public static void checkInfinite(String s)
{
// Boolean flag variable to mark
// if given string is valid
bool flag = true;
int N = s.Length;
// Traverse the given string
for(int i = 0; i < N - 1; i++)
{
// If adjacent character
// differ by 1
if (s[i] == (char)((int)
(s[i + 1]) + 1))
{
continue;
}
// If character 'a' is
// followed by 4
else if (s[i] == 'a' &&
s[i + 1] == 'z')
{
continue;
}
// Else flip the flag and
// break from the loop
else
{
flag = false;
break;
}
}
// Output according to flag variable
if (!flag)
Console.Write("NO");
else
Console.Write("YES");
}
// Driver code
public static void Main(String[] args)
{
// Given string
String s = "ecbaz";
// Function call
checkInfinite(s);
}
}
// This code is contributed by Rajput-Ji
<script>
// Javascript program for the above approach
// Function checks if a given string is
// valid or not and prints the output
function checkInfinite(s)
{
// Boolean flag variable to mark
// if given string is valid
var flag = 1;
var N = s.length;
// Traverse the given string
for (var i = 0; i < N - 1; i++) {
// If adjacent character
// differ by 1
if (s[i] == String.fromCharCode((s[i + 1].charCodeAt(0)) + 1)) {
continue;
}
// If character 'a' is
// followed by 4
else if (s[i] == 'a'
&& s[i + 1] == 'z') {
continue;
}
// Else flip the flag and
// break from the loop
else {
flag = 0;
break;
}
}
// Output according to flag variable
if (flag == 0)
document.write( "NO");
else
document.write( "YES");
}
// Driver Code
// Given string
var s = "ecbaz";
// Function Call
checkInfinite(s);
// This code is contributed by famously.
</script>
Time Complexity: O(N)
Auxiliary Space: O(1)
Approach: Sliding Window
The sliding window approach involves generating a window of size equal to the length of the given string and
slide the window over the infinite string S. At each position of the window, check if the substring of S
starting from that position and of length equal to the length of the given string matches the given string.
If there is a match, return "YES", otherwise continue sliding the window.
Below is the code implementation :
C++
// C++ implementation for the problem
#include <iostream>
#include <string>
using namespace std;
// Function to check if a string is a substring of an infinite length string
bool isSubstring(string str) {
string S = "zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba";
int n = str.length(), m = S.length();
if (n > m) {
return false;
}
for (int i = 0; i <= m - n; i++) {
int j;
for (j = 0; j < n; j++) {
if (S[i+j] != str[j]) {
break;
}
}
if (j == n) {
return true;
}
}
return false;
}
//Driver Code
int main() {
string str = "ywxtuv";
if (isSubstring(str)) {
cout << "YES" << endl;
} else {
cout << "NO" << endl;
}
return 0;
}
public class GFG {
// Function to check if a string is a substring of an infinite length string
public static boolean isSubstring(String str) {
String S = "zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba";
int n = str.length(), m = S.length();
if (n > m) {
return false;
}
for (int i = 0; i <= m - n; i++) {
int j;
for (j = 0; j < n; j++) {
if (S.charAt(i + j) != str.charAt(j)) {
break;
}
}
if (j == n) {
return true;
}
}
return false;
}
//Driver code
public static void main(String[] args) {
String str = "ywxtuv";
if (isSubstring(str)) {
System.out.println("YES");
} else {
System.out.println("NO");
}
}
}
# Function to check if a string is a substring of an infinite length string
def is_substring(s):
infinite_string = "zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba"
n = len(s)
m = len(infinite_string)
# If the input string is longer than the infinite string, it cannot be a substring
if n > m:
return False
# Iterate through the infinite string to check for substring
for i in range(m - n + 1):
j = 0
# Compare each character of the substring with the infinite string
while j < n and infinite_string[i + j] == s[j]:
j += 1
# If j reaches the length of the substring, it means all characters match
if j == n:
return True
# If the loop completes without finding a match, the input string is not a substring
return False
# Driver code
def main():
input_str = "ywxtuv"
if is_substring(input_str):
print("YES")
else:
print("NO")
if __name__ == "__main__":
main()
using System;
namespace SubstringCheckExample
{
class Program
{
// Function to check if a string is a substring of an infinite length string
static bool IsSubstring(string str)
{
// The infinite length string
string S = "zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba";
int n = str.Length; // Length of the input string
int m = S.Length; // Length of the infinite length string
if (n > m)
{
return false; // If the input string is longer than the
// infinite string, it can't be a substring
}
for (int i = 0; i <= m - n; i++)
{
int j;
for (j = 0; j < n; j++)
{
if (S[i + j] != str[j])
{
break; // If characters don't match, exit the inner loop
}
}
if (j == n)
{
return true; // If all characters matched, the input string is a substring
}
}
return false; // If no match was found, the input string is not a substring
}
// Driver Code
static void Main(string[] args)
{
string str = "ywxtuv";
if (IsSubstring(str))
{
Console.WriteLine("YES");
}
else
{
Console.WriteLine("NO");
}
}
}
}
// Function to check if a string is a substring of an infinite length string
function isSubstring(str) {
// Define an infinite-length string 'S'
const S = "zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba";
// Get the lengths of the input 'str' and 'S'
const n = str.length;
const m = S.length;
// Check if the length of 'str' is greater than 'S'
if (n > m) {
return false; // 'str' cannot be a substring
}
// Iterate through 'S' to find possible substrings
for (let i = 0; i <= m - n; i++) {
let j;
// Check characters of 'str' against characters in 'S'
for (j = 0; j < n; j++) {
if (S[i + j] !== str[j]) {
break; // Mismatch found, move to the next substring
}
}
// If we reach the end of 'str', it is a substring
if (j === n) {
return true;
}
}
return false; // 'str' is not a substring of 'S'
}
// Driver code
const str = "ywxtuv";
if (isSubstring(str)) {
console.log("YES"); // Print "YES" if 'str' is a substring
} else {
console.log("NO"); // Print "NO" if 'str' is not a substring
}
Time Complexity: O((m-n+1)*n), where m is the length of the infinite string S and n is the length of the input string str.
Auxiliary Space: O(1)
Similar Reads
Basics & Prerequisites
Data Structures
Array Data StructureIn this article, we introduce array, implementation in different popular languages, its basic operations and commonly seen problems / interview questions. An array stores items (in case of C/C++ and Java Primitive Arrays) or their references (in case of Python, JS, Java Non-Primitive) at contiguous
3 min read
String in Data StructureA string is a sequence of characters. The following facts make string an interesting data structure.Small set of elements. Unlike normal array, strings typically have smaller set of items. For example, lowercase English alphabet has only 26 characters. ASCII has only 256 characters.Strings are immut
2 min read
Hashing in Data StructureHashing is a technique used in data structures that efficiently stores and retrieves data in a way that allows for quick access. Hashing involves mapping data to a specific index in a hash table (an array of items) using a hash function. It enables fast retrieval of information based on its key. The
2 min read
Linked List Data StructureA linked list is a fundamental data structure in computer science. It mainly allows efficient insertion and deletion operations compared to arrays. Like arrays, it is also used to implement other data structures like stack, queue and deque. Here’s the comparison of Linked List vs Arrays Linked List:
2 min read
Stack Data StructureA Stack is a linear data structure that follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). LIFO implies that the element that is inserted last, comes out first and FILO implies that the element that is inserted first
2 min read
Queue Data StructureA Queue Data Structure is a fundamental concept in computer science used for storing and managing data in a specific order. It follows the principle of "First in, First out" (FIFO), where the first element added to the queue is the first one to be removed. It is used as a buffer in computer systems
2 min read
Tree Data StructureTree Data Structure is a non-linear data structure in which a collection of elements known as nodes are connected to each other via edges such that there exists exactly one path between any two nodes. Types of TreeBinary Tree : Every node has at most two childrenTernary Tree : Every node has at most
4 min read
Graph Data StructureGraph Data Structure is a collection of nodes connected by edges. It's used to represent relationships between different entities. If you are looking for topic-wise list of problems on different topics like DFS, BFS, Topological Sort, Shortest Path, etc., please refer to Graph Algorithms. Basics of
3 min read
Trie Data StructureThe Trie data structure is a tree-like structure used for storing a dynamic set of strings. It allows for efficient retrieval and storage of keys, making it highly effective in handling large datasets. Trie supports operations such as insertion, search, deletion of keys, and prefix searches. In this
15+ min read
Algorithms
Searching AlgorithmsSearching algorithms are essential tools in computer science used to locate specific items within a collection of data. In this tutorial, we are mainly going to focus upon searching in an array. When we search an item in an array, there are two most common algorithms used based on the type of input
2 min read
Sorting AlgorithmsA Sorting Algorithm is used to rearrange a given array or list of elements in an order. For example, a given array [10, 20, 5, 2] becomes [2, 5, 10, 20] after sorting in increasing order and becomes [20, 10, 5, 2] after sorting in decreasing order. There exist different sorting algorithms for differ
3 min read
Introduction to RecursionThe process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called a recursive function. A recursive algorithm takes one step toward solution and then recursively call itself to further move. The algorithm stops once we reach the solution
14 min read
Greedy AlgorithmsGreedy algorithms are a class of algorithms that make locally optimal choices at each step with the hope of finding a global optimum solution. At every step of the algorithm, we make a choice that looks the best at the moment. To make the choice, we sometimes sort the array so that we can always get
3 min read
Graph AlgorithmsGraph is a non-linear data structure like tree data structure. The limitation of tree is, it can only represent hierarchical data. For situations where nodes or vertices are randomly connected with each other other, we use Graph. Example situations where we use graph data structure are, a social net
3 min read
Dynamic Programming or DPDynamic Programming is an algorithmic technique with the following properties.It is mainly an optimization over plain recursion. Wherever we see a recursive solution that has repeated calls for the same inputs, we can optimize it using Dynamic Programming. The idea is to simply store the results of
3 min read
Bitwise AlgorithmsBitwise algorithms in Data Structures and Algorithms (DSA) involve manipulating individual bits of binary representations of numbers to perform operations efficiently. These algorithms utilize bitwise operators like AND, OR, XOR, NOT, Left Shift, and Right Shift.BasicsIntroduction to Bitwise Algorit
4 min read
Advanced
Segment TreeSegment Tree is a data structure that allows efficient querying and updating of intervals or segments of an array. It is particularly useful for problems involving range queries, such as finding the sum, minimum, maximum, or any other operation over a specific range of elements in an array. The tree
3 min read
Pattern SearchingPattern searching algorithms are essential tools in computer science and data processing. These algorithms are designed to efficiently find a particular pattern within a larger set of data. Patten SearchingImportant Pattern Searching Algorithms:Naive String Matching : A Simple Algorithm that works i
2 min read
GeometryGeometry is a branch of mathematics that studies the properties, measurements, and relationships of points, lines, angles, surfaces, and solids. From basic lines and angles to complex structures, it helps us understand the world around us.Geometry for Students and BeginnersThis section covers key br
2 min read
Interview Preparation
Practice Problem