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package class17;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.HashMap;
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import java.util.List;
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// 课上讲了哈希表+manacher
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// 有关manacher的解释，看这个帖子 : https://www.mashibing.com/question/detail/56727
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// 从代码层次讲了一下，例子非常详细
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// 测试链接 : https://leetcode.com/problems/palindrome-pairs/
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public class Code03_PalindromePairs1 {
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public static List<List<Integer>> palindromePairs(String[] words) {
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HashMap<String, Integer> wordset = new HashMap<>();
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for (int i = 0; i < words.length; i++) {
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wordset.put(words[i], i);
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}
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List<List<Integer>> res = new ArrayList<>();
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for (int i = 0; i < words.length; i++) {
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res.addAll(findAll(words[i], i, wordset));
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}
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return res;
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}
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public static List<List<Integer>> findAll(String word, int index, HashMap<String, Integer> words) {
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List<List<Integer>> res = new ArrayList<>();
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String reverse = reverse(word);
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Integer rest = words.get("");
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if (rest != null && rest != index && word.equals(reverse)) {
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res.add(Arrays.asList(rest, index));
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res.add(Arrays.asList(index, rest));
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}
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int[] rs = manacherss(word);
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int mid = rs.length >> 1;
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for (int i = 1; i < mid; i++) {
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if (i - rs[i] == -1) {
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rest = words.get(reverse.substring(0, mid - i));
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if (rest != null && rest != index) {
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res.add(Arrays.asList(rest, index));
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}
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}
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}
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for (int i = mid + 1; i < rs.length; i++) {
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if (i + rs[i] == rs.length) {
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rest = words.get(reverse.substring((mid << 1) - i));
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if (rest != null && rest != index) {
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res.add(Arrays.asList(index, rest));
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}
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}
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}
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return res;
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}
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public static int[] manacherss(String word) {
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char[] mchs = manachercs(word);
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int[] rs = new int[mchs.length];
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int center = -1;
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int pr = -1;
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for (int i = 0; i != mchs.length; i++) {
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rs[i] = pr > i ? Math.min(rs[(center << 1) - i], pr - i) : 1;
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while (i + rs[i] < mchs.length && i - rs[i] > -1) {
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if (mchs[i + rs[i]] != mchs[i - rs[i]]) {
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break;
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}
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rs[i]++;
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}
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if (i + rs[i] > pr) {
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pr = i + rs[i];
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center = i;
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}
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}
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return rs;
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}
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public static char[] manachercs(String word) {
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char[] chs = word.toCharArray();
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char[] mchs = new char[chs.length * 2 + 1];
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int index = 0;
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for (int i = 0; i != mchs.length; i++) {
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mchs[i] = (i & 1) == 0 ? '#' : chs[index++];
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}
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return mchs;
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}
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public static String reverse(String str) {
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char[] chs = str.toCharArray();
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int l = 0;
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int r = chs.length - 1;
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while (l < r) {
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char tmp = chs[l];
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chs[l++] = chs[r];
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chs[r--] = tmp;
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}
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return String.valueOf(chs);
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}
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} |
