Grokking the Coding Interview: Patterns for Coding Questions

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String Permutations by changing case (medium)

Problem Statement

Given a string, find all of its permutations preserving the character sequence but changing case.

Example 1:

Input: "ad52"
Output: "ad52", "Ad52", "aD52", "AD52"

Example 2:

Input: "ab7c"
Output: "ab7c", "Ab7c", "aB7c", "AB7c", "ab7C", "Ab7C", "aB7C", "AB7C"

Constraints:

  • 1 <= str.length <= 12
  • str consists of lowercase English letters, uppercase English letters, and digits.

Try it yourself

Try solving this question here:

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Mohammed Dh Abbas

Mohammed Dh Abbas

· 2 years ago

class Solution:
  def findLetterCaseStringPermutations(self, text):
   
    def backtrack(word, result, seen, index):
      result.append(word[:])
      
      for i in range(index, len(word)): # loop through each character in the text
        char = word[i]
       
        if i not in seen and not char.isnumeric(): # if the character is not a number and have no been seen 
          seen.add(i)
          new_word = word[:i] + char.swapcase() + word[i + 1:]
          backtrack(new_word, result, seen, i) # recurse back 
        
          seen.remove(i)

    result = []
    backtrack(text, result, set(), 0)
    return result
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