README_EN.md

2309. Greatest English Letter in Upper and Lower Case

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Description

Given a string of English letters s, return the greatest English letter which occurs as both a lowercase and uppercase letter in s. The returned letter should be in uppercase. If no such letter exists, return an empty string.

An English letter b is greater than another letter a if b appears after a in the English alphabet.

 

Example 1:

Input: s = "lEeTcOdE"
Output: "E"
Explanation:
The letter 'E' is the only letter to appear in both lower and upper case.

Example 2:

Input: s = "arRAzFif"
Output: "R"
Explanation:
The letter 'R' is the greatest letter to appear in both lower and upper case.
Note that 'A' and 'F' also appear in both lower and upper case, but 'R' is greater than 'F' or 'A'.

Example 3:

Input: s = "AbCdEfGhIjK"
Output: ""
Explanation:
There is no letter that appears in both lower and upper case.

 

Constraints:

• 1 <= s.length <= 1000
• s consists of lowercase and uppercase English letters.

Solutions

Python3

class Solution:
    def greatestLetter(self, s: str) -> str:
        ss = set(s)
        for c in ascii_uppercase[::-1]:
            if c in ss and c.lower() in ss:
                return c
        return ''

class Solution:
    def greatestLetter(self, s: str) -> str:
        mask1 = mask2 = 0
        for c in s:
            if c.islower():
                mask1 |= 1 << (ord(c) - ord("a"))
            else:
                mask2 |= 1 << (ord(c) - ord("A"))
        mask = mask1 & mask2
        return chr(mask.bit_length() - 1 + ord("A")) if mask else ""

Java

class Solution {
    public String greatestLetter(String s) {
        Set<Character> ss = new HashSet<>();
        for (char c : s.toCharArray()) {
            ss.add(c);
        }
        for (char a = 'Z'; a >= 'A'; --a) {
            if (ss.contains(a) && ss.contains((char) (a + 32))) {
                return String.valueOf(a);
            }
        }
        return "";
    }
}

class Solution {
    public String greatestLetter(String s) {
        int mask1 = 0, mask2 = 0;
        for (int i = 0; i < s.length(); ++i) {
            char c = s.charAt(i);
            if (Character.isLowerCase(c)) {
                mask1 |= 1 << (c - 'a');
            } else {
                mask2 |= 1 << (c - 'A');
            }
        }
        int mask = mask1 & mask2;
        return mask > 0 ? String.valueOf((char) (31 - Integer.numberOfLeadingZeros(mask) + 'A')) : "";
    }
}

C++

class Solution {
public:
    string greatestLetter(string s) {
        unordered_set<char> ss(s.begin(), s.end());
        for (char c = 'Z'; c >= 'A'; --c) {
            if (ss.count(c) && ss.count(char(c + 32))) {
                return string(1, c);
            }
        }
        return "";
    }
};

class Solution {
public:
    string greatestLetter(string s) {
        int mask1 = 0, mask2 = 0;
        for (char& c : s) {
            if (islower(c)) {
                mask1 |= 1 << (c - 'a');
            } else {
                mask2 |= 1 << (c - 'A');
            }
        }
        int mask = mask1 & mask2;
        return mask ? string(1, 31 - __builtin_clz(mask) + 'A') : "";
    }
};

Go

func greatestLetter(s string) string {
	ss := map[rune]bool{}
	for _, c := range s {
		ss[c] = true
	}
	for c := 'Z'; c >= 'A'; c-- {
		if ss[c] && ss[rune(c+32)] {
			return string(c)
		}
	}
	return ""
}

func greatestLetter(s string) string {
	mask1, mask2 := 0, 0
	for _, c := range s {
		if unicode.IsLower(c) {
			mask1 |= 1 << (c - 'a')
		} else {
			mask2 |= 1 << (c - 'A')
		}
	}
	mask := mask1 & mask2
	if mask == 0 {
		return ""
	}
	return string(byte(bits.Len(uint(mask))-1) + 'A')
}

TypeScript

function greatestLetter(s: string): string {
    const ss = new Array(128).fill(false);
    for (const c of s) {
        ss[c.charCodeAt(0)] = true;
    }
    for (let i = 90; i >= 65; --i) {
        if (ss[i] && ss[i + 32]) {
            return String.fromCharCode(i);
        }
    }
    return '';
}

Rust

impl Solution {
    pub fn greatest_letter(s: String) -> String {
        let mut arr = [0; 26];
        for &c in s.as_bytes().iter() {
            if c >= b'a' {
                arr[(c - b'a') as usize] |= 1;
            } else {
                arr[(c - b'A') as usize] |= 2;
            }
        }
        for i in (0..26).rev() {
            if arr[i] == 3 {
                return char::from(b'A' + i as u8).to_string();
            }
        }
        "".to_string()
    }
}

JavaScript

/**
 * @param {string} s
 * @return {string}
 */
var greatestLetter = function (s) {
    const ss = new Array(128).fill(false);
    for (const c of s) {
        ss[c.charCodeAt(0)] = true;
    }
    for (let i = 90; i >= 65; --i) {
        if (ss[i] && ss[i + 32]) {
            return String.fromCharCode(i);
        }
    }
    return '';
};

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