420. Strong Password Checker LeetCode Solution | Easy Approach

Minimum Cost to Merge Stones

Strong Password Checker A password is considered strong if the below conditions are all met:

  • It has at least 6 characters and at most 20 characters.
  • It contains at least one lowercase letter, at least one uppercase letter, and at least one digit.
  • It does not contain three repeating characters in a row (i.e., "...aaa..." is weak, but "...aa...a..." is strong, assuming other conditions are met).

Given a string password, return the minimum number of steps required to make password strong. if password is already strong, return 0.

In one step, you can:

  • Insert one character to password,
  • Delete one character from password, or
  • Replace one character of password with another character.

Example 1:

Input: password = "a"
Output: 5

Example 2:

Input: password = "aA1"
Output: 3

Example 3:

Input: password = "1337C0d3"
Output: 0


  • 1 <= password.length <= 50
  • password consists of letters, digits, dot '.' or exclamation mark '!'.

Strong Password Checker Solutions

Time: O(n)
Space: O(n)


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