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

• Last Updated : 25 Jan, 2022

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:

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

Please refer complete article on Queries for rotation and Kth character of the given string in constant time for more details!

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