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// @Title: 最长回文子串 (Longest Palindromic Substring)
// @Author: 15816537946@163.com
// @Date: 2020-10-24 11:49:01
// @Runtime: 4 ms
// @Memory: 2.1 MB
impl Solution {
    fn expand_center(s: &[char], left: usize, mut right: usize) -> isize {
        let mut left = left as isize;
        while left >= 0 && right < s.len() && s[left as usize] == s[right] {
            left -= 1;
            right += 1;
        }
        right as isize - left as isize - 1
    }

    pub fn longest_palindrome(s: String) -> String {
        let len = s.len();
        if len < 2 {
            return s;
        }
        let s: Vec<char> = s.chars().collect();
        let mut start = 0;
        let mut end = 0;
        for i in 0..len {
            let len_odd = Solution::expand_center(&s, i, i);
            let len_even = Solution::expand_center(&s, i, i + 1);
            let max_len = len_odd.max(len_even).max(0) as usize;
            if max_len > end - start {
                start = i - (max_len - 1) / 2;
                end = i + max_len / 2;
            }
        }
        s[start..=end].iter().collect()
    }
}
/*
impl Solution {
    /*
    fn helper(s: &str, l: usize, r: usize) -> isize {
        let mut l = l;
        let mut r = r;
        let str_vec: Vec<char> = s.chars().collect();
        while l >= 0 && r < s.len() && str_vec[l] == str_vec[r] {
            l -= 1;
            r += 1;
        }
        r as isize - l as isize - 1
    }
    */
    fn helper(s: &str, left: usize, mut right: usize) -> isize {
        let mut left = left as isize;
        let str_vec: Vec<char> = s.chars().collect();
        while left >= 0 && right < s.len() && str_vec[left as usize] == str_vec[right] {
            left -= 1;
            right += 1;
        }
        right as isize - left as isize - 1
    }

    pub fn longest_palindrome(s: String) -> String {
        if s.len() < 2 {
            return s;
        }

        let (mut lo, mut hi) = (0, 0);

        for i in 0..s.len() {
            let len1 = Solution::helper(&s, i, i);
            let len2 = Solution::helper(&s, i, i + 1);
            let large = len1.max(len2).max(0) as usize;

            if large > hi - lo {
                lo = i - (large - 1) >> 1;
                hi = i + large >> 1;
            }
        }

        String::from(&s[lo..=hi + 1])
    }
}
*/