upload

Author: whd

212 Word Search II .cpp

@@ -0,0 +1,65 @@
+class Solution {
+public:
+    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
+        if (board.empty()) {
+            return vector<string>();
+        }
+        struct Node {
+            Node() {
+                id = -1;
+            }
+            shared_ptr<Node> c[26];
+            int id;
+        };
+        using NodePtr = shared_ptr<Node>;
+        NodePtr root(new Node());
+        auto insert = [&] (const string &s, int id) {
+            NodePtr now = root;
+            for (auto c : s) {
+                c = c - 'a';
+                if (!now->c[c]) {
+                    now->c[c] = NodePtr(new Node());
+                }
+                now = now->c[c];
+            }  
+            now->id = id;
+        };
+        for (int i = 0; i < words.size(); i++) {
+            insert(words[i], i);
+        }
+        unordered_set<int> res_ids;
+        int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
+        int n = board.size(), m = board[0].size();
+        vector<vector<bool>> vis(n, vector<bool>(m, false));
+        function<void(int, int, NodePtr)> dfs = [&] (int x, int y, NodePtr now) {
+            vis[x][y] = true;
+            if (now->id != -1) {
+                res_ids.insert(now->id);
+            }  
+            for (int i = 0; i < 4; i++) {
+                int xx = x + dx[i];
+                int yy = y + dy[i];
+                if (0 <= xx && xx < n && 0 <= yy && yy < m && !vis[xx][yy]) {
+                    auto c = board[xx][yy] - 'a';
+                    if (now->c[c]) {
+                        dfs(xx, yy, now->c[c]);
+                    }
+                }
+            }
+            vis[x][y] = false;
+        };
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                auto c = board[i][j] - 'a';
+                if (root->c[c]) {
+                    dfs(i, j, root->c[c]);
+                }
+            }
+        }
+        vector<string> ans;
+        for (auto id : res_ids) {
+            ans.push_back(words[id]);
+        }
+        return ans;
+    }
+};