Letter Case Permutation

Return a list of all possible strings we could create. Return the output in any order.

 

Example 1:

Input: s = "a1b2"
Output: ["a1b2","a1B2","A1b2","A1B2"]

Example 2:

Input: s = "3z4"
Output: ["3z4","3Z4"]

Solution

/**
 * @param {string} S
 * @return {string[]}
 */
const letterCasePermutation = S => {
  const result = [];
  backtracking(S, 0, '', result);
  return result;
};

const backtracking = (S, i, solution, result) => {
  if (i === S.length) {
    result.push(solution);
    return;
  }

  backtracking(S, i + 1, solution + S[i].toLowerCase(), result);

  if (/[a-zA-Z]/.test(S[i])) {
    backtracking(S, i + 1, solution + S[i].toUpperCase(), result);
  }
};