Update strange-printer-ii.cpp

Author: kamyu104

C++/strange-printer-ii.cpp

@@ -3,6 +3,79 @@
 // Space: O(e)
 
 class Solution {
+public:
+    bool isPrintable(vector<vector<int>>& targetGrid) {
+        unordered_map<int, vector<int>> boxes;
+        for (int r = 0; r < size(targetGrid); ++r) {
+            for (int c = 0; c < size(targetGrid[r]); ++c) {
+                if (!boxes.count(targetGrid[r][c])) {
+                    boxes[targetGrid[r][c]] = {r, c, r, c};
+                } else {
+                    boxes[targetGrid[r][c]][0] = min(boxes[targetGrid[r][c]][0], r);
+                    boxes[targetGrid[r][c]][1] = min(boxes[targetGrid[r][c]][1], c);
+                    boxes[targetGrid[r][c]][2] = max(boxes[targetGrid[r][c]][2], r);
+                    boxes[targetGrid[r][c]][3] = max(boxes[targetGrid[r][c]][3], c);
+                }
+            } 
+        }
+        unordered_map<int, unordered_set<int>> adj;
+        for (const auto& [color, box] : boxes) {
+            for (int r = box[0]; r <= box[2]; ++r) {
+                for (int c = box[1]; c <= box[3]; ++c) {
+                    if (targetGrid[r][c] != color) {
+                        adj[color].emplace(targetGrid[r][c]);
+                    }
+                }
+            }
+        }
+        unordered_map<int, int> lookup;
+        for (const auto& [color, _] : boxes) {
+            if (lookup.count(color)) {
+                continue;
+            }
+            if (hasCycle(adj, color, &lookup)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+private:
+    enum State {VISITING, VISITED};
+
+    bool hasCycle(const unordered_map<int, unordered_set<int>>& adj,
+                  int color,
+                  unordered_map<int, int> *lookup) {
+        vector<pair<int, int>> stk = {{1, color}};
+        while (!empty(stk)) {
+            const auto [step, color] = stk.back(); stk.pop_back();
+            if (step == 1) {
+                (*lookup)[color] = VISITING;
+                stk.emplace_back(2, color);
+                if (!adj.count(color)) {
+                    continue;
+                }
+                for (const auto& new_color : adj.at(color)) {
+                    if (lookup->count(new_color)) {
+                        if ((*lookup)[new_color] == VISITED) {
+                            continue;
+                        }
+                        return true;  // VISITING
+                    }
+                    stk.emplace_back(1, new_color);
+                }
+            } else {
+                (*lookup)[color] = VISITED;
+            }
+        }
+        return false;
+    }
+};
+
+// Time:  O(c * m * n + e), c is the number of colors
+//                        , e is the number of edges in adj, at most O(c^2)
+// Space: O(e)
+class Solution2 {
 public:
     bool isPrintable(vector<vector<int>>& targetGrid) {
         static const int MAX_COLOR = 60;
@@ -49,28 +122,16 @@ class Solution {
     bool hasCycle(const unordered_map<int, unordered_set<int>>& adj,
                   int color,
                   unordered_map<int, int> *lookup) {
-        vector<pair<int, int>> stk = {{1, color}};
-        while (!empty(stk)) {
-            const auto [step, color] = stk.back(); stk.pop_back();
-            if (step == 1) {
-                (*lookup)[color] = VISITING;
-                stk.emplace_back(2, color);
-                if (!adj.count(color)) {
-                    continue;
+        (*lookup)[color] = VISITING;
+        if (adj.count(color)) {
+            for (const auto& new_color : adj.at(color)) {
+                if ((!lookup->count(new_color) && hasCycle(adj, new_color, lookup)) ||
+                    (*lookup)[new_color] == VISITING) {
+                    return true;
                 }
-                for (const auto& new_color : adj.at(color)) {
-                    if (lookup->count(new_color)) {
-                        if ((*lookup)[new_color] == VISITED) {
-                            continue;
-                        }
-                        return true;  // VISITING
-                    }
-                    stk.emplace_back(1, new_color);
-                }
-            } else {
-                (*lookup)[color] = VISITED;
             }
         }
+        (*lookup)[color] = VISITED;
         return false;
     }
 };