How to Print All Permutations of the String in C++

Jinku Hu Feb 02, 2024

C++ C++ String

Use std::next_permutation to Print All Permutations of the String in C++
Use std::prev_permutation to Print All Permutations of the String in C++

How to Print All Permutations of the String in C++

This article will introduce how to print all permutations of the given string in C++.

Use `std::next_permutation` to Print All Permutations of the String in C++

The std:next_permutation algorithm modifies the given range so that the permutation of the elements is ordered lexicographically in ascending order, and a true boolean value is returned if such permutation exists. The function can operate on the std::string object to generate its permutations if the string characters are sorted in descending order. We can utilize std::sort algorithm with std::greater function object to sort the string and then call next_permutation until it returns false. The latter can be implemented using the do...while loop that takes the next_permutation statement as the condition expression and prints the string to the cout stream each cycle.

#include <algorithm>
#include <iostream>
#include <iterator>
#include <limits>

using std::cin;
using std::cout;
using std::endl;
using std::string;

void PrintStringPermutations(string &str) {
  std::sort(str.begin(), str.end(), std::greater<>());

  do {
    cout << str << endl;
  } while (std::next_permutation(str.begin(), str.end()));
}

int main() {
  string input;

  cout << "Enter string to print permutations: ";
  cin >> input;

  PrintStringPermutations(input);

  return EXIT_SUCCESS;
}

Output:

Enter string to print permutations: nel
nle
nel
lne
len
enl
eln

Use `std::prev_permutation` to Print All Permutations of the String in C++

Alternatively, we can utilize another algorithm from STL called - std::prev_permutation that generates the new permutation of the given range with the same lexicographical order but stores the previous permutation when the sequence is provided. The final solution still remains similar to the previous example, except that the prev_permutation function is called in the while loop condition.

#include <algorithm>
#include <iostream>
#include <iterator>
#include <limits>

using std::cin;
using std::cout;
using std::endl;
using std::string;

void PrintStringPermutations(string &str) {
  std::sort(str.begin(), str.end(), std::greater<>());

  do {
    cout << str << endl;
  } while (std::prev_permutation(str.begin(), str.end()));
}

int main() {
  string input;

  cout << "Enter string to print permutations: ";
  cin >> input;

  PrintStringPermutations(input);

  return EXIT_SUCCESS;
}

Output:

Enter string to print permutations: nel
nle
nel
lne
len
enl
eln

Additionally, one can ensure more robust code by implementing the user string validation function that will print the input prompt until the user supplies the valid string. Note that all listed solutions will parse only the single string argument from the command line input, and multi-word strings will not be read.

#include <algorithm>
#include <iostream>
#include <iterator>
#include <limits>

using std::cin;
using std::cout;
using std::endl;
using std::string;

void PrintStringPermutations(string &str) {
  std::sort(str.begin(), str.end(), std::greater<>());

  do {
    cout << str << endl;
  } while (std::prev_permutation(str.begin(), str.end()));
}

template <typename T>
T &validateInput(T &val) {
  while (true) {
    cout << "Enter string to print permutations: ";
    if (cin >> val) {
      break;
    } else {
      if (cin.eof()) exit(EXIT_SUCCESS);
      cout << "Enter string to print permutations\n";
      cin.clear();
      cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }
  }
  return val;
}

int main() {
  string input;

  validateInput(input);
  PrintStringPermutations(input);

  return EXIT_SUCCESS;
}

Output:

Enter string to print permutations: nel
nle
nel
lne
len
enl
eln

Author: Jinku Hu

Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.

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Use std::next_permutation to Print All Permutations of the String in C++

Use std::prev_permutation to Print All Permutations of the String in C++

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Use `std::next_permutation` to Print All Permutations of the String in C++

Use `std::prev_permutation` to Print All Permutations of the String in C++