Create number-of-closed-islands.cpp

Author: kamyu104

C++/number-of-closed-islands.cpp

@@ -0,0 +1,40 @@
+// Time:  O(m * n)
+// Space: O(1)
+
+class Solution {
+public:
+    int closedIsland(vector<vector<int>>& grid) {
+        for (int j = 0; j < grid[0].size(); ++j) {
+            fill(&grid, 0, j);
+            fill(&grid, grid.size() - 1, j);
+        }
+        for (int i = 1; i + 1 < grid.size(); ++i) {
+            fill(&grid, i, 0);
+            fill(&grid, i, grid[0].size() - 1);
+        }
+        int result = 0;
+        for (int i = 1; i + 1 < grid.size(); ++i) {
+            for (int j = 1; j + 1 < grid[0].size(); ++j) {
+                if (fill(&grid, i, j)) {
+                    ++result;
+                }
+            }
+        }
+        return result;
+    }
+
+private:
+    bool fill(vector<vector<int>> *grid, int i, int j) {
+        static vector<pair<int, int>> directions = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
+        if (i < 0 || j < 0 ||
+            i >= grid->size() || j >= (*grid)[i].size() ||
+            (*grid)[i][j]) {
+            return false;
+        }
+        (*grid)[i][j] = 1;
+        for (const auto& [dx, dy] : directions) {
+            fill(grid, i + dx, j + dy);
+        }
+        return true;
+    }
+};