[leetcode]LeetCode刷题的日子--Longest Palindromic Substring

题目：

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.

Example 2:

Input: "cbbd"
Output: "bb"

题目翻译：

很经典的题目，求最长回文字符串

解题思路：

我目前只会使用动态规划的方式进行求解。构建flagslen表格，其中flagsi表示字符串子串(i..j)是否为回文，如果flagi为回文，且flagsi+1，也就是内部子串也为回文的情况下，则认为一定是回文。

代码：

fn longest_palindrome(s: String) -> String {
    let size = s.len();

    if size == 0 {
        return String::from("");
    }

    let mut flags = vec![vec![false; size]; size];

    let mut start = 0;
    let mut max = 1;
    let b = s.as_bytes();

    for i in (0..size) {
        flags[i][i] = true;

        for j in (0..i) {
            flags[j][i] = (b[j] == b[i] && (i-j < 3 || flags[j+1][i-1]));
            if (flags[j][i] && i - j + 1 > max) {
                start = j;
                max = i - j + 1;
            }
        }
    }

    let end = start + max;
    return (s[start as usize..end as usize]).to_string();
}

#[test]
fn test_longest_palindrome() {
    let demo1 = String::from("abcda");
    let ret = longest_palindrome(demo1);
    assert_eq!(ret, "a");
}