#N2068. Check Whether Two Strings are Almost Equivalent
problem link

#solution

class Solution {
    public boolean checkAlmostEquivalent(String word1, String word2) {
        int count[] = new int[26];
        
        for(int i=0; i<word1.length(); i++){
            count[word1.charAt(i)-'a']++;
            count[word2.charAt(i)-'a']--;
        }
        
        for(int i=0; i<26; i++)
            if(Math.abs(count[i]) > 3) return false;
        
        return true;
    }
}

#N231. Power of Two
problem link

#solution

class Solution {
    public boolean isPowerOfTwo(int n) {
        if(n<1) return false;
        if(n==1) return true;
        
        if(n%2==0) return isPowerOfTwo(n/2);
        return false;
    }
}

#N2119. A Number After a Double Reversal
problem link

#solution

class Solution {
    public boolean isSameAfterReversals(int num) {
        return num==0||!(num%10==0);
    }
}

#N2108. Find First Palindromic String in the Array
problem link

#solution

class Solution {
    public String firstPalindrome(String[] words) {
        
        for(String word: words){
            if(check(word))
                return word;
        }
        
        return "";
    }
    
    public boolean check(String word){
        int l = word.length();
        for(int i=0; i<l; i++){
            if(word.charAt(i) != word.charAt(l-i-1))
                return false;
        }
        
        return true;
    }
}

#N1009. Complement of Base 10 Integer
problem link

#solution

class Solution {
    public int bitwiseComplement(int n) {
        if(n==0) return 1;
        int power = 0;
        for(int i=n; i>0; i/=2)
            power++;
        
        int temp=1;
        while(power-- >0)
            temp*=2;
        
        return temp-n-1;
    }
}

#N2124. Check if All A's Appears Before All B's
problem link

#solution

class Solution {
    public boolean checkString(String s) {
        boolean isFound = false;
        
        for(int i=0; i<s.length(); i++){
            if(s.charAt(i) == 'b')
                isFound = true;
            
            if(isFound && s.charAt(i) == 'a')
                return false;
        }
        
        return true;
    }
}

#N884. Uncommon Words from Two Sentences
problem link

#solution

class Solution {
    public String[] uncommonFromSentences(String s1, String s2) {
        Map<String, Integer> map = new HashMap<>();
        for(String word: s1.split(" ")){
            map.put(word, map.getOrDefault(word, 0) +1);
        }
        
        for(String word: s2.split(" ")){
            map.put(word, map.getOrDefault(word, 0) +1);
        }
        
        List<String> list = new ArrayList<>();
        for(Map.Entry<String, Integer> entry: map.entrySet()){
            if(entry.getValue() == 1)
                list.add(entry.getKey());
        }
        
        return list.toArray(new String[0]);
    }
}

#N1694. Reformat Phone Number
problem link

#solution

class Solution {
    public String reformatNumber(String number) {
        StringBuilder sb = new StringBuilder();

        for (char c : number.toCharArray()) {
            if (Character.isDigit(c)) sb.append(c);
        }
        
        int i=0;
        for(; i<sb.length()-4;){
            sb.insert(i+3, '-');
            i+=4;
        }
        
        if(sb.length() - i == 4)
            sb.insert(i+2, '-');
        
        return sb.toString();
    }
}

#N1455. Check If a Word Occurs As a Prefix of Any Word in a Sentence
problem link

#solution

class Solution {
    public int isPrefixOfWord(String sentence, String searchWord) {
        int ans=0;
        for(String word: sentence.split(" ")){
            if(word.startsWith(searchWord))
                return ans+1;
            
            ans++;
        }
        
        return -1;
    }
}

#N1078. Occurrences After Bigram
problem link

#solution

class Solution {
    public String[] findOcurrences(String text, String first, String second) {
        String[] arr=text.split(" ");
        String[] ans = new String[100];
        int count=0;
        for(int i=0; i<arr.length-2; i++){
            if(arr[i].equals(first)&&arr[i+1].equals(second)){
                ans[i]=arr[i+2];
                count ++;
            }
        }
    
        
        String[] main=new String[count];
        
        for(int i=0; i<count; i++){
            for(int j=0; j<ans.length; j++){
                if(ans[j]!=null){
                    main[i]=ans[j];
                    ans[j]=null;
                    break;
                }
            }
        }
        
        return main;
    }
}

#N627. Swap Salary
problem link

#solution

update Salary
set sex = case
sex when 'm' then 'f'
else 'm'
end;

#N181. Employees Earning More Than Their Managers
problem link

#solution

select t1.name as Employee from Employee t1, Employee t2
where t1.managerId = t2.id and t1.salary>t2.salary;

#N2114. Maximum Number of Words Found in Sentences
problem link

#solution

class Solution {
    public int mostWordsFound(String[] sentences) {
        int max = 0;
        for(String str: sentences){
            max = Math.max(max, str.split(" ").length);
        }
        
        return max;
    }
}

#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