#include <iostream>
    #include <string.h>
 
    void reverse(char* begin, const char* const end, char* back) {
        while (begin != end) {
            std::swap(*(begin++), *(--back));
        }
    }
 
	int main(int argc, char** argv)
	{
	    char input[] = "abcdef";
	    size_t len = strlen(input);
	    size_t substrlen = 2;
	    std::cout << input << std::endl;    
	    reverse(input, input + substrlen, input + len);
	    reverse(input + substrlen, input + substrlen, input + len - substrlen);
	    std::cout << input << std::endl;
	    return 0;
	}

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