How to Generate Permutations With Repeated Characters - c++

Question

I basically want to create strings that consist of three operation symbols (eg: +-* or ++/ or +++). Each one of these strings should be pushed into vector <string> opPermutations
This is my code so far:
// Set up permutations for operators
string operatorBank[4] = {"+","-","*","/"};
do {
string currentPerm = operatorBank[0] + operatorBank[1] + operatorBank[2] + operatorBank[3];
this -> opPermutations.push_back(currentPerm);
} while ( std::next_permutation(operatorBank, operatorBank + 4) );
The permutations that are pushed into the vector (as strings) are:
+-*/
+-/*
+/*-
+/-*
-*+/
-*/+
-+*/
-+/*
-/*+
-/+*
/*+-
/*-+
/+*-
/+-*
/-*+
/-+*
What I want however is to have my permutations exist like this:
Each should be three characters in length
Every possible permutation, including the ones in which a character is repeated more than one time, must be present.
I want it to be organized as such:
+++
---
***
///
/*/
+-+
++*
**/
etc...
How can I achieve this?

Answer 1

Using the recursion to print what you asked. Adapting it to store permutation string in vectors should be trivial. I am not a c++ programmer,so there may be better way to do it in C++. but the main idea here is to use recursion.
#include <iostream>
#include <string>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
void displayPermutation(string permutation[], int length){
int i;
for (i=0;i<length;i++){
cout<<permutation[i];
}
cout << endl;
}
void getPermutations(string operatorBank[], int operatorCount,
string permutation[],int permutationLength, int curIndex){
int i;
//stop recursion condition
if(curIndex == permutationLength){
displayPermutation(permutation,permutationLength);
}
else{
for(i = 0; i < operatorCount; i++){
permutation[curIndex] = operatorBank[i];
getPermutations(operatorBank,operatorCount,permutation,
permutationLength,curIndex+1);
}
}
}
int main ()
{
int operatorCount = 4;
int permutationLength = 3;
string operatorBank[] = {"+","-","*","/"};
string permutation[] = {"","","",""}; //empty string
int curIndex = 0;
getPermutations(operatorBank,operatorCount,permutation,
permutationLength,curIndex);
return 0;
}
output:
+++
++-
++*
++/
+-+
+--
+-*
+-/
+*+
+*-
+**
+*/
+/+
+/-
+/*
+//
.
.
and so on.

Answer 2

Strings with repeated elements are not possible permutations, because a permutation is an ordering.
You can do this with 3 nested for loops as wlyles said.
Edited to add:
This will print the strings I think you want. You can replace the cout statement with opPermutations.push_back(operatorBank[i]+operatorBank[j]+operatorBank[k]) to add to the vector.
#include <iostream>
#include <string>
int main(){
std::string operatorBank[4] = {"+","-","*","/"};
for (int i=0; i<4; ++i){
for (int j=0; j<4; ++j){
for (int k=0; k<4; ++k){
std::cout << operatorBank[i] << operatorBank[j] << operatorBank[k] << std::endl;
}
}
}
return 0;
}
I think maybe the confusion is over the term "permutation." You could get the same strings as 3-permutations of the set {"+","+","+","-","-","-","*","*","*","/","/","/"} but using loops seems simpler to me.

Answer 3

Easiest way to generate permutations is Set Product ..
list<string> setProduct (list<string> a, list<string> b)
{
list<string> L;
list<string>::iterator i, j;
for(i = a.begin(); i != a.end(); ++i)
for(j = b.begin(); j != b.end(); ++j)
L.push_front(*i + *j);
return L;
}
list<string> permute (list<string> a, int len)
{
list<string> L;
while (len --> 0) L.splice(a.end(), setProduct(L,a));
return L;
}