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 Kth 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: 2nd character is d
Query 3: str = “ghabcdef”
Query 4: 7th 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 Kth character can be found by str[(ptr + K – 1) % N].
Below is the implementation of the above approach:
Javascript
<script>// Javascript implementation of the approachvar size = 2;// Function to perform the required// queries on the given stringfunction 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 codevar 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> |
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!
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