README_EN.md

409. Longest Palindrome

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Description

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters.

Letters are case sensitive, for example, "Aa" is not considered a palindrome here.

 

Example 1:

Input: s = "abccccdd"
Output: 7
Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7.

Example 2:

Input: s = "a"
Output: 1
Explanation: The longest palindrome that can be built is "a", whose length is 1.

 

Constraints:

• 1 <= s.length <= 2000
• s consists of lowercase and/or uppercase English letters only.

Solutions

Python3

class Solution:
    def longestPalindrome(self, s: str) -> int:
        n = len(s)
        counter = Counter(s)
        odd_cnt = sum(e % 2 for e in counter.values())
        return n if odd_cnt == 0 else n - odd_cnt + 1

Java

class Solution {
    public int longestPalindrome(String s) {
        int[] counter = new int[128];
        for (char c : s.toCharArray()) {
            ++counter[c];
        }
        int oddCnt = 0;
        for (int e : counter) {
            oddCnt += (e % 2);
        }
        int n = s.length();
        return oddCnt == 0 ? n : n - oddCnt + 1;
    }
}

TypeScript

function longestPalindrome(s: string): number {
    let n = s.length;
    let ans = 0;
    let record = new Array(128).fill(0);
    for (let i = 0; i < n; i++) {
        record[s.charCodeAt(i)]++;
    }
    for (let i = 65; i < 128; i++) {
        let count = record[i];
        ans += count % 2 == 0 ? count : count - 1;
    }
    return ans < s.length ? ans + 1 : ans;
}

function longestPalindrome(s: string): number {
    const map = new Map();
    for (const c of s) {
        map.set(c, (map.get(c) ?? 0) + 1);
    }
    let hasOdd = false;
    let res = 0;
    for (const v of map.values()) {
        res += v;
        if (v & 1) {
            hasOdd = true;
            res--;
        }
    }
    return res + (hasOdd ? 1 : 0);
}

C++

class Solution {
public:
    int longestPalindrome(string s) {
        vector<int> counter(128);
        for (char c : s) ++counter[c];
        int oddCnt = 0;
        for (int e : counter) oddCnt += e % 2;
        int n = s.size();
        return oddCnt == 0 ? n : n - oddCnt + 1;
    }
};

Go

func longestPalindrome(s string) int {
	counter := make([]int, 128)
	for _, c := range s {
		counter[c]++
	}
	oddCnt := 0
	for _, e := range counter {
		oddCnt += e % 2
	}
	n := len(s)
	if oddCnt == 0 {
		return n
	}
	return n - oddCnt + 1
}

Rust

use std::collections::HashMap;

impl Solution {
    pub fn longest_palindrome(s: String) -> i32 {
        let mut map: HashMap<char, i32> = HashMap::new();
        for c in s.chars() {
            map.insert(c, map.get(&c).unwrap_or(&0) + 1);
        }
        let mut has_odd = false;
        let mut res = 0;
        for v in map.values() {
            res += v;
            if v % 2 == 1 {
                has_odd = true;
                res -= 1;
            }
        }
        res + if has_odd { 1 } else { 0 }
    }
}

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