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#include "leetcode.h"

class Solution {
public:
  int numIslands(vector<vector<char>> &grid) {
    int islands = 0;
    for (int i = 0; i < grid.size(); i++) {
      for (int j = 0; j < grid[0].size(); j++) {
        if (grid[i][j] == '1') {
          dfs(grid, i, j);
          ++islands;
        }
      }
    }
    return islands;
  }

private:
  void dfs(vector<vector<char>> &grid, int i, int j) {
    if (i < 0 || i >= grid.size() || j < 0 || j >= grid[0].size())
      return;
    if (grid[i][j] == '2' || grid[i][j] == '0')
      return;
    grid[i][j] = '2';
    dfs(grid, i + 1, j);
    dfs(grid, i, j + 1);
    dfs(grid, i - 1, j);
    dfs(grid, i, j + 1);
  }
};