README_EN.md

2309. Greatest English Letter in Upper and Lower Case

中文文档

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 ''

Java

class Solution {
    public String greatestLetter(String s) {
        int[] cnt = new int[26];
        for (char c : s.toCharArray()) {
            if (Character.isLowerCase(c)) {
                cnt[c - 'a'] |= 1;
            } else if (Character.isUpperCase(c)) {
                cnt[c - 'A'] |= 2;
            }
        }
        for (int i = 25; i >= 0; --i) {
            if (cnt[i] == 3) {
                return String.valueOf((char) ('A' + i));
            }
        }
        return "";
    }
}

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 "";
    }
}

C++

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

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 ""
}

TypeScript

function greatestLetter(s: string): string {
    let couter = new Array(128).fill(false);
    for (let char of s) {
        couter[char.charCodeAt(0)] = true;
    }
    for (let i = 90; i >= 65; i--) {
        if (couter[i] && couter[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()
    }
}

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