0420-StrongPasswordChecker.cs

//-----------------------------------------------------------------------------
// Runtime: 72ms
// Memory Usage: 21.9 MB
// Link: https://leetcode.com/submissions/detail/372034527/
//-----------------------------------------------------------------------------

using System;
using System.Text;

namespace LeetCode
{
    public class _0420_StrongPasswordChecker
    {
        public int StrongPasswordChecker(string s)
        {
            if (string.IsNullOrEmpty(s)) return 6;

            var length = s.Length;
            var sb = new StringBuilder();
            sb.Append(s[0]);
            for (int i = 1; i < length; i++)
            {
                if (s[i] != s[i - 1])
                    sb.Append(' ');
                sb.Append(s[i]);
            }

            bool hasDigit = false, hasLower = false, hasUpper = false;
            int replacements = 0;
            var replace = new int[3] { 0, 0, 0 };
            var words = sb.ToString().Split();
            foreach (var word in words)
            {
                var ch = word[0];
                hasDigit = hasDigit || char.IsDigit(ch);
                hasLower = hasLower || char.IsLower(ch);
                hasUpper = hasUpper || char.IsUpper(ch);

                replacements += word.Length / 3;
                if (word.Length >= 3)
                    replace[word.Length % 3]++;
            }

            var deletions = Math.Max(0, length - 20);
            var additions = Math.Max((hasDigit ? 0 : 1) + (hasLower ? 0 : 1) + (hasUpper ? 0 : 1), 6 - length);

            var d = deletions;
            replacements -= Math.Min(replace[0], d);
            d = Math.Max(d - replace[0], 0);
            replacements -= Math.Min(replace[1], d / 2);
            d = Math.Max(d - replace[1] * 2, 0);
            replacements -= d / 3;

            return deletions + Math.Max(replacements, additions);
        }
    }
}