impl number of islands

leetcode-cc/NumOfIslands.hpp

@@ -1,4 +1,5 @@
 #include <unordered_set>
+#include <utility>
 
 #include "PairHash.h"
 #include "TestHelper.h"
@@ -23,21 +24,60 @@ class SNumOfIslands : public ISolution {
   int test() const override {
     return testHelper<vector<vector<char>>, int>(
         {{
-            {'1', '1', '1', '1', '0'},
-            {'1', '1', '0', '1', '0'},
-            {'1', '1', '0', '0', '0'},
-            {'0', '0', '0', '0', '0'},
-        }},
-        {1}, [this](auto input) { return this->numIslands(input); });
+             {'1', '1', '1', '1', '0'},
+             {'1', '1', '0', '1', '0'},
+             {'1', '1', '0', '0', '0'},
+             {'0', '0', '0', '0', '0'},
+         },
+         {
+             {'1', '1', '0', '0', '0'},
+             {'1', '1', '0', '0', '0'},
+             {'0', '0', '1', '0', '0'},
+             {'0', '0', '0', '1', '1'},
+         }},
+        {1, 3}, [this](auto input) { return this->numIslands(input); });
   };
   int benchmark() const override { return 0; }
 
  private:
   int numIslands(vector<vector<char>>& grid) const {
     int m = grid.size();
     int n = grid[0].size();
+
+    pair<int, int> p = {0, 0};
+
+    while (p.first < m && p.second < n) {
+      if (grid[p.first][p.second] == '1') break;
+      p = nextPair(p, m, n);
+    }
+
+    int res = 0;
+    unordered_set<pair<int, int>, pair_hash> set = {};
+
+    while (p.first < m && p.second < n) {
+      if (!set.contains(p) && grid[p.first][p.second] == '1') {
+        dfs(grid, p.first, p.second, set);
+        res++;
+      }
+      p = nextPair(p, m, n);
+    }
+
+    return res;
   }
 
   static void dfs(vector<vector<char>>& grid, int row, int col,
-                  unordered_set<pair<int, int>, pair_hash>) {}
+                  unordered_set<pair<int, int>, pair_hash>& set) {
+    if (!set.contains({row, col}) && grid[row][col] == '1') {
+      set.insert({row, col});
+      if (row > 0) dfs(grid, row - 1, col, set);
+      if (row < grid.size() - 1) dfs(grid, row + 1, col, set);
+      if (col > 0) dfs(grid, row, col - 1, set);
+      if (col < grid[0].size() - 1) dfs(grid, row, col + 1, set);
+    }
+  }
+
+  static pair<int, int> nextPair(pair<int, int> p, int m, int n) {
+    return (p.second == n - 1) ? make_pair(p.first + 1, 0)
+                               : make_pair(p.first, p.second + 1);
+  }
 };