Create regions-cut-by-slashes.cpp

Author: kamyu104

C++/regions-cut-by-slashes.cpp

@@ -0,0 +1,71 @@
+// Time:  O(n^2)
+// Space: O(n^2)
+
+class Solution {
+public:
+    int regionsBySlashes(vector<string>& grid) {
+        UnionFind union_find(grid.size() * grid.size() * 4);
+        for (int i = 0; i < grid.size(); ++i) {
+            for (int j = 0; j < grid[0].size(); ++j) {
+                if (i) {
+                    union_find.union_set(index(grid.size(), i - 1, j, S),
+                                         index(grid.size(),i, j, N));
+                }
+                if (j) {
+                    union_find.union_set(index(grid.size(), i, j - 1, E),
+                                         index(grid.size(), i, j, W));
+                }
+                if (grid[i][j] != '/') {
+                    union_find.union_set(index(grid.size(), i, j, N),
+                                         index(grid.size(), i, j, E));
+                    union_find.union_set(index(grid.size(), i, j, S),
+                                         index(grid.size(), i, j, W));
+                }
+                if (grid[i][j] != '\\') {
+                    union_find.union_set(index(grid.size(), i, j, W),
+                                         index(grid.size(), i, j, N));
+                    union_find.union_set(index(grid.size(), i, j, E),
+                                         index(grid.size(), i, j, S));
+                }
+            }
+        }
+        return union_find.size();
+    }
+    
+private:
+    enum NODES {N, E, S, W};
+    
+    class UnionFind {
+        public:
+            UnionFind(const int n) : set_(n), count_(n) {
+                iota(set_.begin(), set_.end(), 0);
+            }
+
+            int find_set(const int x) {
+               if (set_[x] != x) {
+                   set_[x] = find_set(set_[x]);  // Path compression.
+               }
+               return set_[x];
+            }
+
+            void union_set(const int x, const int y) {
+                int x_root = find_set(x), y_root = find_set(y);
+                if (x_root != y_root) {
+                    set_[min(x_root, y_root)] = max(x_root, y_root);
+                    --count_;
+                }
+            }
+
+            int size() const {
+                return count_;
+            }
+
+        private:
+            vector<int> set_;
+            int count_;
+    };
+    
+    int index(int n, int i, int j, int k) {
+        return (i * n + j) * 4 + k;
+    }
+};