README.md

1542. Find Longest Awesome Substring

You are given a string s. An awesome substring is a non-empty substring of s such that we can make any number of swaps in order to make it a palindrome.

Return the length of the maximum length awesome substring of s.

Example 1:

Input: s = "3242415"
Output: 5
Explanation: "24241" is the longest awesome substring, we can form the palindrome "24142" with some swaps.

Example 2:

Input: s = "12345678"
Output: 1

Example 3:

Input: s = "213123"
Output: 6
Explanation: "213123" is the longest awesome substring, we can form the palindrome "231132" with some swaps.

Constraints:

• 1 <= s.length <= 105
• s consists only of digits.

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn longest_awesome(s: String) -> i32 {
        let mut hash = HashMap::from([(0, -1)]);
        let mut x = 0;
        let mut ret = 1;

        for (i, digit) in s.bytes().enumerate() {
            x ^= 1 << (digit - b'0');
            ret = ret.max(i as i32 - hash.get(&x).unwrap_or(&(i as i32)));
            for digit in 0..10 {
                ret = ret.max(i as i32 - hash.get(&(x ^ (1 << digit))).unwrap_or(&(i as i32)));
            }
            if !hash.contains_key(&x) {
                hash.insert(x, i as i32);
            }
        }

        ret
    }
}