212:单词搜索 II（抄官网）

src/main/java/leetcode/editor/cn/WordSearchIi.java

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+//给定一个 m x n 二维字符网格 board 和一个单词（字符串）列表 words，找出所有同时在二维网格和字典中出现的单词。 
+//
+// 单词必须按照字母顺序，通过 相邻的单元格 内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母在一个单词中不允许被重复使
+//用。 
+//
+// 
+//
+// 示例 1： 
+//
+// 
+//输入：board = [["o","a","a","n"],["e","t","a","e"],["i","h","k","r"],["i","f",
+//"l","v"]], words = ["oath","pea","eat","rain"]
+//输出：["eat","oath"]
+// 
+//
+// 示例 2： 
+//
+// 
+//输入：board = [["a","b"],["c","d"]], words = ["abcb"]
+//输出：[]
+// 
+//
+// 
+//
+// 提示： 
+//
+// 
+// m == board.length 
+// n == board[i].length 
+// 1 <= m, n <= 12 
+// board[i][j] 是一个小写英文字母 
+// 1 <= words.length <= 3 * 10⁴ 
+// 1 <= words[i].length <= 10 
+// words[i] 由小写英文字母组成 
+// words 中的所有字符串互不相同 
+// 
+// Related Topics 字典树 数组 字符串 回溯 矩阵 👍 531 👎 0
+
+package leetcode.editor.cn;
+
+import java.util.*;
+
+//212:单词搜索 II
+class WordSearchIi {
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new WordSearchIi().new Solution();
+    }
+
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+    class Solution {
+        int[][] dirs = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
+
+        public List<String> findWords(char[][] board, String[] words) {
+            Trie trie = new Trie();
+            for (String word : words) {
+                trie.insert(word);
+            }
+            Set<String> ans = new HashSet<String>();
+            for (int i = 0; i < board.length; ++i) {
+                for (int j = 0; j < board[0].length; ++j) {
+                    dfs(board, trie, i, j, ans);
+                }
+            }
+            return new ArrayList<String>(ans);
+        }
+
+        public void dfs(char[][] board, Trie now, int i1, int j1, Set<String> ans) {
+            if (!now.children.containsKey(board[i1][j1])) {
+                return;
+            }
+            char ch = board[i1][j1];
+            now = now.children.get(ch);
+            if (!"".equals(now.word)) {
+                ans.add(now.word);
+            }
+            board[i1][j1] = '#';
+            for (int[] dir : dirs) {
+                int i2 = i1 + dir[0], j2 = j1 + dir[1];
+                if (i2 >= 0 && i2 < board.length && j2 >= 0 && j2 < board[0].length) {
+                    dfs(board, now, i2, j2, ans);
+                }
+            }
+            board[i1][j1] = ch;
+        }
+    }
+
+    class Trie {
+        String word;
+        Map<Character, Trie> children;
+        boolean isWord;
+
+        public Trie() {
+            this.word = "";
+            this.children = new HashMap<Character, Trie>();
+        }
+
+        public void insert(String word) {
+            Trie cur = this;
+            for (int i = 0; i < word.length(); ++i) {
+                char c = word.charAt(i);
+                if (!cur.children.containsKey(c)) {
+                    cur.children.put(c, new Trie());
+                }
+                cur = cur.children.get(c);
+            }
+            cur.word = word;
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}

src/main/java/leetcode/editor/cn/doc/content/WordSearchIi.md

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+<p>给定一个 <code>m x n</code> 二维字符网格 <code>board</code><strong> </strong>和一个单词（字符串）列表 <code>words</code>，找出所有同时在二维网格和字典中出现的单词。</p>
+
+<p>单词必须按照字母顺序，通过 <strong>相邻的单元格</strong> 内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母在一个单词中不允许被重复使用。</p>
+
+<p> </p>
+
+<p><strong>示例 1：</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2020/11/07/search1.jpg" style="width: 322px; height: 322px;" />
+<pre>
+<strong>输入：</strong>board = [["o","a","a","n"],["e","t","a","e"],["i","h","k","r"],["i","f","l","v"]], words = ["oath","pea","eat","rain"]
+<strong>输出：</strong>["eat","oath"]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2020/11/07/search2.jpg" style="width: 162px; height: 162px;" />
+<pre>
+<strong>输入：</strong>board = [["a","b"],["c","d"]], words = ["abcb"]
+<strong>输出：</strong>[]
+</pre>
+
+<p> </p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li><code>m == board.length</code></li>
+	<li><code>n == board[i].length</code></li>
+	<li><code>1 <= m, n <= 12</code></li>
+	<li><code>board[i][j]</code> 是一个小写英文字母</li>
+	<li><code>1 <= words.length <= 3 * 10<sup>4</sup></code></li>
+	<li><code>1 <= words[i].length <= 10</code></li>
+	<li><code>words[i]</code> 由小写英文字母组成</li>
+	<li><code>words</code> 中的所有字符串互不相同</li>
+</ul>
+<div><div>Related Topics</div><div><li>字典树</li><li>数组</li><li>字符串</li><li>回溯</li><li>矩阵</li></div></div><br><div><li>👍 531</li><li>👎 0</li></div>