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# Queries for rotation and Kth character of the given string in constant time

• Difficulty Level : Easy
• Last Updated : 10 May, 2021

Given a string str, the task is to perform the following type of queries on the given string:

1. (1, K): Left rotate the string by K characters.
2. (2, K): Print the Kth character of the string.

Examples:

Input: str = “abcdefgh”, q[][] = {{1, 2}, {2, 2}, {1, 4}, {2, 7}}
Output:

Query 1: str = “cdefghab”
Query 2: 2nd character is d
Query 3: str = “ghabcdef”
Query 4: 7th character is e
Input: str = “abc”, q[][] = {{1, 2}, {2, 2}}
Output:

Approach: The main observation here is that the string doesn’t need to be rotated in every query instead we can create a pointer ptr pointing to the first character of the string and which can be updated for every rotation as ptr = (ptr + K) % N where K the integer by which the string needs to be rotated and N is the length of the string. Now for every query of the second type, the Kth character can be found by str[(ptr + K – 1) % N].
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `#define size 2` `// Function to perform the required``// queries on the given string``void` `performQueries(string str, ``int` `n,``                    ``int` `queries[][size], ``int` `q)``{` `    ``// Pointer pointing to the current starting``    ``// character of the string``    ``int` `ptr = 0;` `    ``// For every query``    ``for` `(``int` `i = 0; i < q; i++) {` `        ``// If the query is to rotate the string``        ``if` `(queries[i] == 1) {` `            ``// Update the pointer pointing to the``            ``// starting character of the string``            ``ptr = (ptr + queries[i]) % n;``        ``}``        ``else` `{` `            ``int` `k = queries[i];` `            ``// Index of the kth character in the``            ``// current rotation of the string``            ``int` `index = (ptr + k - 1) % n;` `            ``// Print the kth character``            ``cout << str[index] << ``"\n"``;``        ``}``    ``}``}` `// Driver code``int` `main()``{``    ``string str = ``"abcdefgh"``;``    ``int` `n = str.length();` `    ``int` `queries[][size] = { { 1, 2 }, { 2, 2 },``                            ``{ 1, 4 }, { 2, 7 } };``    ``int` `q = ``sizeof``(queries) / ``sizeof``(queries);` `    ``performQueries(str, n, queries, q);` `    ``return` `0;``}`

## Java

 `// Java implementation of the above approach``import` `java.util.*;``class` `GFG``{``static` `int` `size = ``2``;` `// Function to perform the required``// queries on the given string``static` `void` `performQueries(String str, ``int` `n,``                           ``int` `queries[][], ``int` `q)``{` `    ``// Pointer pointing to the current``    ``// starting character of the string``    ``int` `ptr = ``0``;` `    ``// For every query``    ``for` `(``int` `i = ``0``; i < q; i++)``    ``{` `        ``// If the query is to rotate the string``        ``if` `(queries[i][``0``] == ``1``)``        ``{` `            ``// Update the pointer pointing to the``            ``// starting character of the string``            ``ptr = (ptr + queries[i][``1``]) % n;``        ``}``        ``else``        ``{``            ``int` `k = queries[i][``1``];` `            ``// Index of the kth character in the``            ``// current rotation of the string``            ``int` `index = (ptr + k - ``1``) % n;` `            ``// Print the kth character``            ``System.out.println(str.charAt(index));``        ``}``    ``}``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``String str = ``"abcdefgh"``;``    ``int` `n = str.length();` `    ``int` `queries[][] = { { ``1``, ``2` `}, { ``2``, ``2` `},``                        ``{ ``1``, ``4` `}, { ``2``, ``7` `} };``    ``int` `q = queries.length;` `    ``performQueries(str, n, queries, q);``}``}` `// This code is contributed by 29AjayKumar`

## Python3

 `# Python3 implementation of the approach``size ``=` `2` `# Function to perform the required``# queries on the given string``def` `performQueries(string, n, queries, q) :` `    ``# Pointer pointing to the current starting``    ``# character of the string``    ``ptr ``=` `0``;` `    ``# For every query``    ``for` `i ``in` `range``(q) :` `        ``# If the query is to rotate the string``        ``if` `(queries[i][``0``] ``=``=` `1``) :` `            ``# Update the pointer pointing to the``            ``# starting character of the string``            ``ptr ``=` `(ptr ``+` `queries[i][``1``]) ``%` `n;``            ` `        ``else` `:` `            ``k ``=` `queries[i][``1``];` `            ``# Index of the kth character in the``            ``# current rotation of the string``            ``index ``=` `(ptr ``+` `k ``-` `1``) ``%` `n;` `            ``# Print the kth character``            ``print``(string[index]);` `# Driver code``if` `__name__ ``=``=` `"__main__"` `:` `    ``string ``=` `"abcdefgh"``;``    ``n ``=` `len``(string);` `    ``queries ``=` `[[ ``1``, ``2` `], [ ``2``, ``2` `],``               ``[ ``1``, ``4` `], [ ``2``, ``7` `]];``    ``q ``=` `len``(queries);` `    ``performQueries(string, n, queries, q);``    ` `# This code is contributed by AnkitRai01`

## C#

 `// C# implementation of the approach``using` `System;``    ` `class` `GFG``{``static` `int` `size = 2;` `// Function to perform the required``// queries on the given string``static` `void` `performQueries(String str, ``int` `n,``                           ``int` `[,]queries, ``int` `q)``{` `    ``// Pointer pointing to the current``    ``// starting character of the string``    ``int` `ptr = 0;` `    ``// For every query``    ``for` `(``int` `i = 0; i < q; i++)``    ``{` `        ``// If the query is to rotate the string``        ``if` `(queries[i, 0] == 1)``        ``{` `            ``// Update the pointer pointing to the``            ``// starting character of the string``            ``ptr = (ptr + queries[i, 1]) % n;``        ``}``        ``else``        ``{``            ``int` `k = queries[i, 1];` `            ``// Index of the kth character in the``            ``// current rotation of the string``            ``int` `index = (ptr + k - 1) % n;` `            ``// Print the kth character``            ``Console.WriteLine(str[index]);``        ``}``    ``}``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``String str = ``"abcdefgh"``;``    ``int` `n = str.Length;` `    ``int` `[,]queries = { { 1, 2 }, { 2, 2 },``                       ``{ 1, 4 }, { 2, 7 } };``    ``int` `q = queries.GetLength(0);` `    ``performQueries(str, n, queries, q);``}``}` `// This code is contributed by PrinciRaj1992`

## Javascript

 ``
Output:
```d
e```

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