【牛客網】密碼截取 (即: 找到字符串中對稱子串的最大長度)

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import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            String str = in.next();
            int len = str.length();
            int res = 0;
            // 做法是從第一個字符遍歷
            //          從最後一個字符向前遍歷，
            for (int i = 0; i < len; i++) {
                for (int j = len - 1; j > i; j--) {
                    // 頭是第i個字符
                    // 尾是第j個字符
                    int tmp = 0;
                    int left = i;
                    int right = j;
                    while (left < right && str.charAt(left) == str.charAt(right)) {
                        tmp += 2;
                        left++;
                        right--;
                    }
                    if (left >= right) {// 說明一直進行地不錯
                        if (left == right) {
                            tmp++;
                        }
                        res = Math.max(res, tmp);
                    }
                }
            }
            System.out.println(res);
        }
    }
}