分割两个字符串得到回文串

/*
 * 思路：
 * 使用Java Stream API遍历字符串的所有可能分割点，检查是否存在组合为回文的情况。
 * 为了代码简洁和演示目的，尽量使用 Stream 和 Lambda 表达式来实现。
 */

import java.util.stream.IntStream;

public class Solution {
    public boolean checkPalindromeFormation(String a, String b) {
        return check(a, b) || check(b, a);
    }

    private boolean check(String a, String b) {
        int n = a.length();
        return IntStream.range(0, n).anyMatch(i -> isPalindrome(a.substring(i, n) + b.substring(0, i)) || isPalindrome(b.substring(i, n) + a.substring(0, i)));
    }

    private boolean isPalindrome(String s) {
        return new StringBuilder(s).reverse().toString().equals(s);
    }
}

The solution first defines a helper function `check(a, b)` that checks if `a` and `b` can form a palindrome by splitting at the same index. It starts by comparing characters from the outer edges towards the center. If the characters at positions `i` and `j` are the same, it moves inward. When it encounters characters that don't match, it takes the substring from `i` to `j` (inclusive) from both strings and checks if either substring is a palindrome. If either is a palindrome, it means a palindrome can be formed by combining the prefixes and suffixes of `a` and `b`. The main function calls `check(a, b)` and `check(b, a)` to cover both possibilities of forming a palindrome and returns `true` if either call returns `true`.

O(n)

O(n)