#N595. Big Countries
problem link

#solution

select name, population, area from World
where area >= 3000000 || population >= 25000000;

memory usage of all database problems in leetcode is 0. so weird🤔

#N1179. Reformat Department Table
problem link

#solution

select id,
sum(if(month='Jan', revenue, null)) as Jan_Revenue,
sum(if(month='Feb', revenue, null)) as Feb_Revenue,
sum(if(month='Mar', revenue, null)) as Mar_Revenue,
sum(if(month='Apr', revenue, null)) as Apr_Revenue,
sum(if(month='May', revenue, null)) as May_Revenue,
sum(if(month='Jun', revenue, null)) as Jun_Revenue,
sum(if(month='Jul', revenue, null)) as Jul_Revenue,
sum(if(month='Aug', revenue, null)) as Aug_Revenue,
sum(if(month='Sep', revenue, null)) as Sep_Revenue,
sum(if(month='Oct', revenue, null)) as Oct_Revenue,
sum(if(month='Nov', revenue, null)) as Nov_Revenue,
sum(if(month='Dec', revenue, null)) as Dec_Revenue
from department
group by id
order by id

#N1408. String Matching in an Array
problem link

#solution

class Solution {
    public List<String> stringMatching(String[] words) {
        HashSet<String> set = new HashSet<>();
        
        for(int i=0; i<words.length-1; i++){
            for(int j=i+1; j<words.length; j++){
                if(words[i].contains(words[j]))
                    set.add(words[j]);
                
                if(words[j].contains(words[i]))
                    set.add(words[i]);
            }
        }
        
        return new ArrayList<String>(set);
    }
}

#N1189. Maximum Number of Balloons
problem link

#solution

class Solution {
    public int maxNumberOfBalloons(String text) {
        int letters[] = new int[26];
        for(char ch: text.toCharArray())
            letters[ch-'a']++;
        
        int min = letters[1];
        min = Math.min(min, letters[0]);
        min = Math.min(min, letters[11]/2);
        min = Math.min(min, letters[14]/2);
        min = Math.min(min, letters[13]);
        
        return min;
    }
}

#statistics
Till this time, 223 in total,
210 easy;
13 medium;
type of problem solutions have been posted

#N1945. Sum of Digits of String After Convert
problem link

#solution

class Solution {
    public int getLucky(String s, int k) {
        StringBuilder sb=new StringBuilder();

        for(int i=0;i<s.length();i++)
        sb.append((s.charAt(i)-'a')+1);
        String result=sb.toString();
 
        if(result.length()==1)
        return Character.getNumericValue(result.charAt(0));
        
        int sum=0;
        while(k-->0 && result.length()>1)
        {   
            sum=0;
            for(int i=0;i<result.length();i++)
            sum+=Character.getNumericValue(result.charAt(i));
            
            result=String.valueOf(sum);
        }
        
        return sum;   
    }
}

#N1507. Reformat Date
problem link

#solution

class Solution {
    public String reformatDate(String date) {
        StringBuilder sb = new StringBuilder();
        String month[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
        String d[] = date.split(" ");
        sb.append(d[2]+"-");
        for(int i=0; i<12; i++)
            if(month[i].equals(d[1])){
                if(i<9) sb.append(0).append(i+1);
                else sb.append(i+1);
            }
        sb.append("-");
        if(d[1].substring(0, d[0].length()-2).length()==1)
            sb.append(0).append(d[0].charAt(0));
        else
            sb.append(d[0].substring(0, 2));
        
        return sb.toString();
    }
}

#N242. Valid Anagram
problem link

#solution

class Solution {
    public boolean isAnagram(String s, String t) {
        if(s.length() != t.length()) return 0==1;
        Map<Character, Integer> mapS = new HashMap<>();
        Map<Character, Integer> mapT = new HashMap<>();
        
        for(int i=0; i<s.length(); i++){
            mapS.put(s.charAt(i), mapS.getOrDefault(s.charAt(i), 0) +1);
            mapT.put(t.charAt(i), mapT.getOrDefault(t.charAt(i), 0) +1);
        }
        
        return mapS.equals(mapT);
    }
}

#N620. Not Boring Movies
problem link

#solution

select * from cinema
where description <> 'boring' and id%2=1
order by rating desc;

#N175. Combine Two Tables
problem link

#solution

select t1.firstname, t1.lastname, t2.city, t2.state
from person t1 left join address t2
on t1.personid=t2.personid;

#N182. Duplicate Emails
problem link

#solution

select email from
(select email, count(email) as num from person group by email) as temp
where num>1;

#N183. Customers Who Never Order
problem link

#solution

select name as 'customers' from customers
where id not in
(select customerid from orders);

#N196. Delete Duplicate Emails
problem link

#solution

delete p1.*
from person p1, person p2
where p1.email=p2.email and p1.id>p2.id;

#N197. Rising Temperature
problem link

#solution

select w1.id from weather w1, weather w2
where datediff(w1.recorddate, w2.recorddate)=1 and
w1.temperature>w2.temperature;

#N596. Classes More Than 5 Students
problem link

#solution

select class from(select class, count(class) as num from courses group by class) as temp where num>4;

#N2129. Capitalize the Title
problem link

#solution

class Solution {
    public String capitalizeTitle(String title) {
        StringBuilder sb = new StringBuilder();
        for(String s: title.split(" ")){
            if(s.length()>2)
                sb.append(s.substring(0, 1).toUpperCase()).append(s.substring(1).toLowerCase());
            else
                sb.append(s.toLowerCase());
            
            sb.append(" ");
        }
        
        return sb.toString().trim();
    }
}

#N1869. Longer Contiguous Segments of Ones than Zeros
problem link

#solution

class Solution {
    public boolean checkZeroOnes(String s) {
        String[] one=s.split("0");
        String[] zero=s.split("1");
        
        int max0=0, max1=0;
        for(String str: one)
            max1=Math.max(max1, str.length());
        
        for(String str: zero)
            max0=Math.max(max0, str.length());
        
        return max1>max0;
    }
}

#N171. Excel Sheet Column Number
problem link

#solution

class Solution {
    public int titleToNumber(String columnTitle) {
        int num=0;
        char[] title = columnTitle.toCharArray();
        int length=title.length;
        for(char ch: title)
            num = num*26+(ch-'A'+1);
        
        return num;
    }
}

#N1422. Maximum Score After Splitting a String
problem link

#solution

class Solution {
    public int maxScore(String s) {
        int zeros = 0, ones = 0, max = Integer.MIN_VALUE;
      for(int i=0;i<s.length();i++) {
        if(s.charAt(i) == '0') zeros++; else ones++;
        if(i != s.length()-1) max = Math.max(zeros - ones, max);
      }
      return max + ones;
    }
}