String permutations

OSCC · JavaScript, String, Recursion · Nov 15, 2020

Generates all permutations of a string (contains duplicates).

  • Use recursion.
  • For each letter in the given string, create all the partial permutations for the rest of its letters.
  • Use Array.prototype.map() to combine the letter with each partial permutation.
  • Use Array.prototype.reduce() to combine all permutations in one array.
  • Base cases are for String.prototype.length equal to 2 or 1.
  • ⚠️ WARNING: The execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your environment to hang as it tries to solve all the different combinations.
const stringPermutations = str => {
  if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
  return str
    .split('')
    .reduce(
      (acc, letter, i) =>
        acc.concat(
          stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(
            val => letter + val
          )
        ),
      []
    );
};
stringPermutations('abc'); // ['abc', 'acb', 'bac', 'bca', 'cab', 'cba']

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