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

Last Updated : 09 Jun, 2022

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

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

Examples:

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

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 K^th character can be found by str[(ptr + K - 1) % N].
Below is the implementation of the above approach:

JavaScript

<script>

// Javascript implementation of the approach

var size = 2;

// Function to perform the required
// queries on the given string
function performQueries(str, n, queries, q)
{

    // Pointer pointing to the current starting
    // character of the string
    var ptr = 0;

    // For every query
    for (var 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 {

            var k = queries[i][1];

            // Index of the kth character in the
            // current rotation of the string
            var index = (ptr + k - 1) % n;

            // Print the kth character
            document.write( str[index] + "<br>");
        }
    }
}

// Driver code
var str = "abcdefgh";
var n = str.length;
var queries = [ [ 1, 2 ], [ 2, 2 ], 
                        [ 1, 4 ], [ 2, 7 ] ];
var q = queries.length;
performQueries(str, n, queries, q);

</script>

Output:

d
e

Time Complexity: O(Q) , Where Q is the number of queries
Auxiliary Space: O(1)

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

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

kartik

Improve

Article Tags :

Practice Tags :

Strings

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

Similar Reads

Thank You!

What kind of Experience do you want to share?