1254. Number of Closed Islands

Given a 2D grid consists of 0s (land) and 1s (water).  An island is a maximal 4-directionally connected group of 0s and a closed island is an island totally (all left, top, right, bottom) surrounded by 1s.

Return the number of closed islands.

Author: SteffiKeranJ

closed.cpp

@@ -0,0 +1,33 @@
+class Solution {
+public:
+    int closedIsland(vector<vector<int>>& grid) {
+        if(grid.empty() || grid[0].empty()) return 0;
+        int h = grid.size();
+        int w = grid[0].size();
+        int count = 0;
+        int i,j;
+        for(i=0; i < h; ++i) {
+            for (j=0; j < w; ++j){
+                if(grid[i][j]==0) {
+                    count+=dfs(grid, i , j)?1:0;
+                }
+            }
+        }
+        return count;
+    }
+
+    private:
+    bool dfs(vector<vector<int>>&grid, int i, int j) {
+        if (i < 0 || j < 0|| i >= grid.size() || j >= grid[0].size()) {
+            return false;
+        }
+        if (grid[i][j]==1) return true;
+        grid[i][j] = 1;
+        bool d1 = dfs(grid, i+1, j);
+        bool d2 = dfs(grid, i-1, j);
+        bool d3 = dfs(grid, i, j+1);
+        bool d4 = dfs(grid, i, j-1);
+        return d1 && d2 && d3 && d4;
+
+    }
+};