update

hard/212.word-search-ii.java

@@ -16,33 +16,32 @@ class Solution {
         root = new TrieNode();
         root.cnt = -1;
         for (String word : words) root.insert(word);
-        boolean[][] used = new boolean[n][m];
         for (int y = 0; y < n; y++) {
             for (int x = 0; x < m; x++) {
                 StringBuilder sb = new StringBuilder();
-                backtrack(y, x, root, sb, used, res);
+                backtrack(y, x, root, sb, res);
             }
         }
         return res;
     }
 
-    private void backtrack(int y, int x, TrieNode curr, StringBuilder sb, boolean[][] used, LinkedList<String> res) {
+    private void backtrack(int y, int x, TrieNode curr, StringBuilder sb, LinkedList<String> res) {
         if (curr == null || curr.cnt == 0) return;
         if (curr.isKey) {
             res.add(sb.toString());
             root.remove(sb.toString());
         }
-        if (y < 0 || n <= y || x < 0 || m <= x || used[y][x]) return;
-        char c = board[y][x];
+        char c;
+        if (y < 0 || n <= y || x < 0 || m <= x || (c = board[y][x]) == '#') return;
         sb.append(c);
-        used[y][x] = true;
+        board[y][x] = '#';
         curr = curr.next[(int) c - 'a'];
         for (int i = 0; i < 4; i++) {
             int ny = y + dy[i], nx = x + dx[i];
-            backtrack(ny, nx, curr, sb, used, res);
+            backtrack(ny, nx, curr, sb, res);
         }
         sb.deleteCharAt(sb.length() - 1);
-        used[y][x] = false;
+        board[y][x] = c;
     }
 
     class TrieNode {