Reverse a string at every nth occurance in it [closed] - c++

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I have a string str[]="ABCDEFGHI" and say n=3. I need to implement reversestring(arr,n) logic for any input string, for any value of n. In this case, my output has to be str = "CBAFEDIHG"
If my str[]="PQRSTUVWXYZ", for n=4, my output has to be str = "SRQPWVUTXYZ". In such cases,you can ignore reversing the last occurrence, as there are less than 4 letters.
Could the similar logic be generalised for input[]="this is a simple test", output[]="sith si a elpmis tset" without using any nth occurrence condition using function overloading in c++.

Answer 1

Assuming that you are dealing with C-style strings, if you want to reverse every n characters you can simply do something along the lines of the following:
//Iterators
int x, y;
char str[] = "ABCDEFGHI";
int n = 3;
int strLen = strlen(str);
//Assuming C99+ for variable length arrays...
char newStr[strLen + 1];
if (strLen % n != 0) {
printf("For this simple example the length of str must be a multiple of n\n");
return 0;
}
for (x = 0; x < strLen; x += n) {
for (y = 0; y < n; y++) {
newStr[x + y] = str[x + (n - y) - 1];
}
}
//Ensure string is terminated properly
newStr[strLen] = 0;
printf("Converted %s to %s\n", str, newStr);
return 0;
In terms of generalising this, the second example you give involves reversing words, rather than blocks of n characters, so you therefore need a different approaching of splitting the string at separate words and reversing those chunks, which is a different problem

Answer 2

Here's an example of using only one library function, std::reverse:
#include <iostream>
#include <algorithm>
int main() {
std::string s1 = "ABCDEFGHI";
std::string s1_output = "CBAFEDIHG";
std::string s2 = "PQRSTUVWXYZ";
std::string s2_output = "SRQPWVUTXYZ";
int N1 = 3;
int N2 = 4;
for (unsigned int i = 0; i < s1.size() / N1; i++)
std::reverse(s1.begin() + (i * N1), s1.begin() + (i * N1 + N1));
std::cout << std::boolalpha << (s1 == s1_output) << std::endl; // true
for (unsigned int i = 0; i < s2.size() / N2; i++)
std::reverse(s2.begin() + (i * N2), s2.begin() + (i * N2 + N2));
std::cout << std::boolalpha << (s2 == s2_output) << std::endl; // true
}
Your second example is different from your first example, because you're operating on individual words, and not a range. It is also different because you don't ignore chunks that are smaller than N.
As suggested in the comments, you can use std::istringstream and use the extraction operator, to extract "chunks" inbetween whitespace.
#include <iostream>
#include <algorithm>
#include <sstream>
#include <iterator>
int main() {
std::string s1 = "this is a simple test";
std::string s1_output = "siht si a elpmis tset"; // you made a typo
std::istringstream iss(s1);
std::string chunk;
std::string output = "";
while (iss >> chunk) {
std::reverse(chunk.begin(), chunk.end());
output += chunk + " ";
}
output.erase(output.size() - 1, output.size()); // chop off remaining space
std::cout << std::boolalpha << (output == s1_output); // true
}