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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.
1#include <string>
#include <algorithm>
std::string reverseString(const std::string& s, int k) {
std::string result = s;
for (size_t start = 0; start < result.size(); start += 2 * k) {
auto end = std::min(start + k, result.size());
std::reverse(result.begin() + start, result.begin() + end);
}
return result;
}
int main() {
std::string s = "abcdefg";
int k = 2;
std::cout << reverseString(s, k); // Output: "bacdfeg"
return 0;
}This C++ solution leverages std::string directly, while using std::reverse for inversion within calculated bounds of the current target chunk. This simplifies the logic by letting STL handle lower-level operations.