Palindrome Pairs 超时代码

import javax.swing.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class Solution {
    private final long MOD = 1000000007;
    private final int maxn = 300 + 100;
    private long[] pow = new long[maxn];

    public List<List<Integer>> palindromePairs(String[] words) {
        pow[0] = 1;
        for (int i = 1; i < maxn; ++i) {
            pow[i] = pow[i - 1] * 26 % MOD;
        }

        List<Long> hash1 = Arrays.stream(words).map(word -> {
            long hash = 0;
            for (int i = 0; i < word.length(); ++i) {
                hash = (hash * 26 + word.charAt(i) - 'a' + 1) % MOD;
            }
            return hash;
        }).collect(Collectors.toList());
        List<Long> hash2 = Arrays.stream(words).map(word -> {
            long hash = 0;
            for (int i = word.length() - 1; i >= 0; --i) {
                hash = (hash * 26 + word.charAt(i) - 'a' + 1) % MOD;
            }
            return hash;
        }).collect(Collectors.toList());

        List<List<Integer>> ans = new ArrayList<>();
        for (int i = 0; i < words.length; ++i) {
            for (int j = 0; j < words.length; ++j) {
                if (i == j) {
                    continue;
                }
                if ((hash1.get(i) * pow[words[j].length()] % MOD + hash1.get(j)) % MOD ==
                        (hash2.get(j) * pow[words[i].length()] % MOD + hash2.get(i)) % MOD) {
                    ans.add(Stream.of(i, j).collect(Collectors.toList()));
                }
            }
        }
        return ans;
    }
}