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package class26;
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.LinkedList;
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import java.util.List;
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// 本题测试链接 : https://leetcode.com/problems/word-search-ii/
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public class Code02_WordSearchII {
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public static class TrieNode {
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public TrieNode[] nexts;
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public int pass;
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public boolean end;
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public TrieNode() {
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nexts = new TrieNode[26];
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pass = 0;
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end = false;
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}
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}
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public static void fillWord(TrieNode head, String word) {
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head.pass++;
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char[] chs = word.toCharArray();
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int index = 0;
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TrieNode node = head;
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for (int i = 0; i < chs.length; i++) {
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index = chs[i] - 'a';
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if (node.nexts[index] == null) {
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node.nexts[index] = new TrieNode();
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}
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node = node.nexts[index];
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node.pass++;
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}
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node.end = true;
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}
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public static String generatePath(LinkedList<Character> path) {
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char[] str = new char[path.size()];
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int index = 0;
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for (Character cha : path) {
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str[index++] = cha;
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}
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return String.valueOf(str);
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}
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public static List<String> findWords(char[][] board, String[] words) {
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TrieNode head = new TrieNode(); // 前缀树最顶端的头
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HashSet<String> set = new HashSet<>();
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for (String word : words) {
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if (!set.contains(word)) {
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fillWord(head, word);
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set.add(word);
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}
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}
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// 答案
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List<String> ans = new ArrayList<>();
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// 沿途走过的字符，收集起来，存在path里
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LinkedList<Character> path = new LinkedList<>();
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for (int row = 0; row < board.length; row++) {
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for (int col = 0; col < board[0].length; col++) {
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// 枚举在board中的所有位置
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// 每一个位置出发的情况下，答案都收集
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process(board, row, col, path, head, ans);
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}
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}
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return ans;
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}
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// 从board[row][col]位置的字符出发，
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// 之前的路径上，走过的字符，记录在path里
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// cur还没有登上，有待检查能不能登上去的前缀树的节点
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// 如果找到words中的某个str，就记录在 res里
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// 返回值，从row,col 出发，一共找到了多少个str
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public static int process(
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char[][] board, int row, int col,
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LinkedList<Character> path, TrieNode cur,
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List<String> res) {
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char cha = board[row][col];
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if (cha == 0) { // 这个row col位置是之前走过的位置
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return 0;
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}
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// (row,col) 不是回头路 cha 有效
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int index = cha - 'a';
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// 如果没路，或者这条路上最终的字符串之前加入过结果里
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if (cur.nexts[index] == null || cur.nexts[index].pass == 0) {
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return 0;
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}
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// 没有走回头路且能登上去
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cur = cur.nexts[index];
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path.addLast(cha);// 当前位置的字符加到路径里去
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int fix = 0; // 从row和col位置出发，后续一共搞定了多少答案
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// 当我来到row col位置，如果决定不往后走了。是不是已经搞定了某个字符串了
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if (cur.end) {
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res.add(generatePath(path));
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cur.end = false;
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fix++;
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}
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// 往上、下、左、右，四个方向尝试
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board[row][col] = 0;
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if (row > 0) {
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fix += process(board, row - 1, col, path, cur, res);
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}
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if (row < board.length - 1) {
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fix += process(board, row + 1, col, path, cur, res);
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}
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if (col > 0) {
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fix += process(board, row, col - 1, path, cur, res);
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}
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if (col < board[0].length - 1) {
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fix += process(board, row, col + 1, path, cur, res);
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}
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board[row][col] = cha;
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path.pollLast();
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cur.pass -= fix;
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return fix;
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}
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}
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