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:
# 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 |
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!