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.

思路：小于6的情况可以简单求得，关键在于大于20，并有多个重复的情况。需要把重复子串数量存储起来。观察可得，当大于20时，删除操作优先作用于重复个数%3==0子串的情况，再是%3==1子串的情况，再是%3==2子串的情况，（以上操作基于贪心思想，为了之后的替换操作最少）。

class Solution {
    public int strongPasswordChecker(String s) {
        int len=s.length();
        if(len<=3) return 6-len;
        boolean f1=false,f2=false,f3=false;
        List<Integer> rec=new ArrayList<>();
        int remain=s.length()-20;//还能删除的个数
        int re=remain;
        for(int i=0;i<len;i++){
            if('0'<=s.charAt(i)&&s.charAt(i)<='9') f1=true;
            if('a'<=s.charAt(i)&&s.charAt(i)<='z') f2=true;
            if('A'<=s.charAt(i)&&s.charAt(i)<='Z') f3=true;
            int cnt=1;
            while(i<s.length()-1&&s.charAt(i)==s.charAt(i+1)){
                cnt++;
                i++;
            }
            if(cnt>=3){
                if(remain>0){
                    if(cnt%3==0){
                        cnt--;
                        remain--;
                    }
                }
                if(cnt>=3)rec.add(cnt);
            }
        }
        int c=3;
        if(f1) c--;
        if(f2) c--;
        if(f3) c--;
        if(s.length()==4) return Math.max(2,c);
        if(s.length()==5) return Math.max(1,c);
        //检查重复,先删除，后替换
        for(int i=0;i<rec.size();i++){ //%3=1
            if(remain==1){
                remain=0;
                break;
            }
            if(remain>0&&rec.get(i)%3==1){
                int n=rec.get(i);
                rec.set(i,n-2);
                remain-=2;
            }
            
        }
        for(int i=0;i<rec.size();i++){ //%3=2
            if(remain==2||remain==1){
                remain=0;
                break;
            }
            if(remain>0){
                int n=rec.get(i);
                if(n>3){
                    int r=n-2;
                    rec.set(i,n-Math.min(remain,r));
                    remain=Math.max(remain-r,0);
                }
            }
        }
        int res=re-remain;
        if(remain>0) return res+c+remain;//删除余下的
        for(int a:rec){//替换
            res+=a/3;
            c-=a/3;
        }
        return res+(c>0?c:0);
    }
}