Thảo luận các easy problems trên leetcode.com

Ref: https://leetcode.com/problemset/all/?difficulty=EASY&page=1

Thành tích

Top	Thành viên	Hoàn thành
1	Quang	1, 2
2	Thịnh Lớn	3, 6
3	Quý	4
4	Khoa	5

Vấn đề

1. https://leetcode.com/problems/second-largest-digit-in-a-string/

Member: Quang

Submission: https://leetcode.com/submissions/detail/787843585/

Language: Java

class Solution {
    public int secondHighest(String s) {
        int len = s.length();

        int max = -1;
        int secondMax = -1;

        for(int i = 0; i < len; ++i){
            final char ch = s.charAt(i);
            if(ch >= '0' && ch <= '9') {
                int num = ch - '0';

                if(max == -1 && secondMax == -1) {
                    max = num;
                    secondMax = num;
                } else if(max < num){
                    secondMax = max;
                    max = num;
                } else if(num < max) {
                    if(max == secondMax) secondMax = num;
                    else if(secondMax < num) secondMax = num;
                }

            }
        }

        return max == secondMax ? -1 : secondMax;
    }
}

1. https://leetcode.com/problems/detect-pattern-of-length-m-repeated-k-or-more-times/

Member: Quang

Submission: https://leetcode.com/submissions/detail/795397090/

Language: PHP

class Solution {

    /**
     * @param Integer[] $arr
     * @param Integer $m
     * @param Integer $k
     * @return Boolean
     */
    function containsPattern($arr, $m, $k) {
        $splitItem = 0;

        for ($i = $m; $i < count($arr); $i++) {
            if($arr[$i] !== $arr[$i - $m]) {
                $splitItem = 0;
            } else {
                if(++$splitItem === $m * ($k - 1)) {
                    return true;
                }
            }
        }
        return false;
    }
}

1. https://leetcode.com/problems/reverse-vowels-of-a-string/

Member: Thịnh Lớn

Submission: https://leetcode.com/submissions/detail/798642454/

Language: PHP

class Solution {

    /**
     * @param String $s
     * @return String
     */
    function reverseVowels($s) {
        $len = strlen($s);
        if ($len < 2) {
            return $s;
        }

        $vowels = [];
        for($i = 0; $i < $len; $i++) {
            if ($s[$i] === 'a' 
                || $s[$i] === 'e' 
                || $s[$i] === 'i' 
                || $s[$i] === 'o' 
                || $s[$i] === 'u'
                || $s[$i] === 'A' 
                || $s[$i] === 'E' 
                || $s[$i] === 'I' 
                || $s[$i] === 'O' 
                || $s[$i] === 'U'
               )             
            {
                $vowels[] = $i; 
            }
        }

        $vowelsLen = count($vowels);
        if ($vowelsLen < 2) {
            return $s;
        }

        for($i = 0; $i < $vowelsLen/2; $i++) {
            $middle = $s[$vowels[$i]];
            $s[$vowels[$i]] = $s[$vowels[$vowelsLen - $i - 1]];
            $s[$vowels[$vowelsLen - $i - 1]] = $middle;
        }
        return $s;
    }
}

1. https://leetcode.com/problems/count-the-number-of-consistent-strings/

Member: Qúy

Submission: https://leetcode.com/submissions/detail/800328356/

Language: PHP

// WAY 1 - readable way
class Solution {

    /**
     * @param String $allowed
     * @param String[] $words
     * @return Integer
     */
    function countConsistentStrings($allowed, $words) {
        $count = 0;
        $test1 = count_chars($allowed,1);
        foreach($words as $word){
            $test2 = count_chars($word,1);
            if(empty(array_diff_key($test2, $test1))){
                $count++;
            }
        }
        return $count;
    }
}

// WAY 2 - performance way ? Sometimes timerun as same as WAY 1
class Solution {

    /**
     * @param String $allowed
     * @param String[] $words
     * @return Integer
     */
    function countConsistentStrings($allowed, $words) {
        $count = count($words);
        foreach($words as $word){
            for($i = 0; $i < strlen($word); $i++){
                if(strpos($allowed,$word[$i]) === false) { // avoid position = 0
                    $count--;
                    break;
                }
            }
        }
        return $count;
    }
}

• Other fancy solution in Python

Member: a Huy

class Solution:
    def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
      return sum([1 for word in words if set(word).issubset(set(allowed))])

1. https://leetcode.com/problems/the-latest-login-in-2020/

Member: Khoa

Submission: https://leetcode.com/submissions/detail/803507835/

Language: SQL

# 1
select user_id, max(time_stamp) as last_stamp
from Logins
where year(time_stamp) = 2020
group by user_id;

# 2
select L1.user_id, L1.time_stamp as last_stamp
from Logins L1
left join Logins L2
    on L2.user_id = L1.user_id 
        and L2.time_stamp > L1.time_stamp 
        and year(L2.time_stamp) = 2020
where year(L1.time_stamp) = 2020
    and L2.user_id is null;

# 3
select L1.user_id, L1.time_stamp as last_stamp
from Logins L1
where year(L1.time_stamp) = 2020 
    and not exists (select 1 
                    from Logins L2 
                    where L2.user_id = L1.user_id 
                        and L2.time_stamp > L1.time_stamp 
                        and year(L2.time_stamp) = 2020
                    order by time_stamp desc 
                    limit 1);

1. https://leetcode.com/problems/number-of-strings-that-appear-as-substrings-in-word/

Member: Thịnh Lớn

Submission: https://leetcode.com/submissions/detail/804326676/

Language: PHP

class Solution {

    /**
     * @param String[] $patterns
     * @param String $word
     * @return Integer
     */
    function numOfStrings($patterns, $word) {
        $sum = 0;
        foreach($patterns as $pattern) {
            if (strpos($word, $pattern) !== false) $sum++;
        }
        return $sum;
    }
}

1. https://leetcode.com/problems/article-views-i/

2. To be continued