
Problem Statement
The task is to manipulate a given string s
based on an integer k
. The string manipulation involves reversing specific parts of the string. Specifically, for every segment of 2k
characters in the string:
- Reverse the first
k
characters. - The next
k
characters remain unchanged.
However, if the length of the remaining part of the string is less than 2k
but at least k
, only the first k
characters are reversed and the rest are left as they are. If the remaining characters are fewer than k
, all of them are reversed. This procedure provides a new version of the string based on the specified rules.
Examples
Example 1
Input:
s = "abcdefg", k = 2
Output:
"bacdfeg"
Example 2
Input:
s = "abcd", k = 2
Output:
"bacd"
Constraints
1 <= s.length <= 104
s
consists of only lowercase English letters.1 <= k <= 104
Approach and Intuition
The solution to this problem involves repeated segments of the string based on the value of k
. Here's a step-by-step approach:
- Initialize an empty string to collect the result.
- Use a loop to process each segment of up to
2k
characters:- For the first half (
k
characters) of any complete2k
segment:- Reverse these
k
characters. - Append this reversed section to the result string.
- Reverse these
- For the second half (
k
characters) of the segment (if it exists):- Append these characters as they are to the result string.
- For the first half (
- If a segment is less than
2k
but at leastk
:- Reverse only the first
k
characters and leave the rest as original.
- Reverse only the first
- If the segment is less than
k
:- Reverse all the characters in this segment.
- Continue this until the entire string has been processed.
This systematic approach allows the string to be manipulated exactly as specified, by treating it in discrete chunks and applying different rules based on the chunk's size relative to k
.
Solutions
- Java
class Solution {
public String reverseStringK(String str, int k) {
char[] charArray = str.toCharArray();
for (int start = 0; start < charArray.length; start += 2 * k) {
int left = start, right = Math.min(start + k - 1, charArray.length - 1);
while (left < right) {
char temp = charArray[left];
charArray[left++] = charArray[right];
charArray[right--] = temp;
}
}
return new String(charArray);
}
}
The provided Java solution defines a method reverseStringK
that takes a string and an integer k
as parameters. This method reverses every k
characters in the string at alternately spaced intervals. Here's a brief rundown on how the function operates:
- Convert the input string into a character array for mutable operations.
- Iterate through the character array using a loop. The loop steps are set to
2 * k
to ensure that every alternate block ofk
characters is reversed. - Inside the loop, use two pointers,
left
andright
, initialized to frame the current block of characters to reverse (left
at the starting position of the block andright
at the minimum ofstart + k - 1
and the last index of the array). - A nested while loop swaps characters between the
left
andright
pointers, effectively reversing the portion of the array between these pointers. - Convert the modified character array back to a string before returning it.
The method is efficient in reversing the specified portions of the string and preserves the order of characters outside of the specified boundaries. Make sure to use this function to handle strings where specific segments need to be reversed, seamlessly integrating into broader string manipulation tasks.
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