## Challenges - Permutation Challenge SolutionString Permutation Challenge Solution The trick to string permutations is to find all permutations that begin with one letter, then all permutations that begin with a second letter, and so forth. This might suggest a recursive solution: in order to find all permutations that begin with a given letter, call permute on the remainder of the string, thereby finding all permutations of the substring using the same algorithm. One way of coding this is as follows: #include <iostream> #include <string> using namespace std; string swtch(string topermute, int x, int y) { string newstring = topermute; newstring[x] = newstring[y]; newstring[y] = topermute[x]; //avoids temp variable return newstring; } void permute(string topermute, int place) { if(place == topermute.length() - 1) { cout<<topermute<<endl; } for(int nextchar = place; nextchar < topermute.length(); nextchar++) { permute(swtch(topermute, place, nextchar), place+1); } } int main(int argc, char* argv[]) { if(argc!=2) { cout<<"Proper input is 'permute string'"; return 1; } permute(argv[1], 0); }Many other solutions exist! If yours doesn't match the Cprogramming.com key, but it still works, let us know and we'll upload it as an alternative answer. For instance, if you have a solution that doesn't use the string library, or if you use only C i/o, let us know so that we can upload it as an example for those who haven't learned about certain topics. |