420. Strong Password Checker

A password is considered strong if below conditions are all met:

1. It has at least 6 characters and at most 20 characters.
2. It must contain at least one lowercase letter, at least one uppercase letter, and at least one digit.
3. It must NOT contain three repeating characters in a row ("...aaa..." is weak, but "...aa...a..." is strong, assuming other conditions are met).

Write a function strongPasswordChecker(s), that takes a string s as input, and return the MINIMUM change required to make s a strong password. If s is already strong, return 0.

Insertion, deletion or replace of any one character are all considered as one change.

摘自

https://discuss.leetcode.com/topic/64511/java-with-detailed-explanation

public class Solution {    public int strongPasswordChecker(String s){int len=s.length();int neededNum=getNeededNum(s);if(len<6)return Math.max(6-len, neededNum);ArrayList<Integer> groups=new ArrayList<>();GeneralGroups(groups, s);if(s.length()<=20){int replace=0;for(int num :groups)replace+=num/3;return Math.max(replace, neededNum);}Collections.sort(groups);int charCount=0;int n=0;while(charCount<20&&n<groups.size()){charCount+=groups.get(n);n++;}while(groups.size()>n)groups.remove(groups.size()-1);charCount=0;int badGroups=0;for(int i=0;i<groups.size();i++){if(groups.get(i)>20)groups.set(i, 20);charCount+=groups.get(i);if(groups.get(i)>2)badGroups++;}int deletion=len-20;int toDelete=charCount-20;int remainder=0;while(toDelete>0&&badGroups>0){for(int i=0;i<n;i++){int count=groups.get(i);if(count>2&&count%3==remainder){int del=Math.min(toDelete, remainder+1);groups.set(i, count-del);toDelete-=del;if(groups.get(i)<=2)badGroups--;if(toDelete==0||badGroups==0)break;}}remainder=(remainder+1)%3;}int replace=0;for(int group : groups)replace+=group/3;return deletion+Math.max(replace, neededNum);}public int getNeededNum(String s){boolean lower=false,upper=false,digit=false;for(int i=0;i<s.length();i++){char c=s.charAt(i);lower=lower||(c>='a'&&c<='z');upper=upper||(c>='A'&&c<='Z');digit=digit||(c>='0'&&c<='9');}return (lower?0:1)+(upper?0:1)+(digit?0:1);}public void GeneralGroups(ArrayList<Integer> groups,String s){for(int i=0;i<s.length();){char c=s.charAt(i);int j=i+1;while(j<s.length())if(s.charAt(j)==c)j++;else {break;}groups.add(j-i);i=j;}}}