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In this approach, we directly manipulate the string representation by considering it as a character array (or list in some languages) for in-place modification. We handle the string in chunks of 2k and reverse the first k characters of each chunk.
Time Complexity: O(n), where n is the length of the string.
Space Complexity: O(1), as we are reversing in place.
1#include <stdio.h>
2#include <string.h>
3
4void reverseString(char* s, int k) {
5 int length = strlen(s);
6 for (int start = 0; start < length; start += 2 * k) {
7 int i = start, j = (start + k - 1 < length) ? start + k - 1 : length - 1;
8 while (i < j) {
9 // Swap characters
10 char temp = s[i];
11 s[i++] = s[j];
12 s[j--] = temp;
13 }
14 }
15}
16
17int main() {
18 char s[] = "abcdefg";
19 int k = 2;
20 reverseString(s, k);
21 printf("%s", s); // Output: "bacdfeg"
22 return 0;
23}This C program utilizes a function reverseString which modifies the string s in place. It processes segments of length 2k, reversing the first k characters within each segment. The main function demonstrates an example with s = "abcdefg" and k = 2.
In this approach, we use a StringBuilder (or equivalent structure in the respective programming languages) to construct the final output. This approach is effective because handling mutable strings directly supports efficient character manipulation operations.
Time Complexity: O(n), where n is the length of the string.
Space Complexity: O(1) as we operate directly on the input array.
1using System;
using System.Text;
public class Solution {
public static string ReverseString(string s, int k) {
var stringBuilder = new StringBuilder(s);
for (int start = 0; start < s.Length; start += 2 * k) {
int end = Math.Min(start + k, s.Length);
string reversedPart = new string(s.Substring(start, end - start).ToCharArray().Reverse().ToArray());
stringBuilder.Remove(start, end - start).Insert(start, reversedPart);
}
return stringBuilder.ToString();
}
public static void Main() {
string s = "abcdefg";
int k = 2;
Console.WriteLine(ReverseString(s, k)); // Output: "bacdfeg"
}
}This C# solution uses StringBuilder for mutable string operations. It manages the reversal logic by first creating a reversed substring and then integrating it back into the builder efficiently.