before 5 pm challenge: https://leetcode.com/problems/number-of-islands/

number-of-islands.cpp

class Solution {
public:
    int solve(vector<vector<char>>& grid, int r, int c) {
        if (!(r >= 0 && r < grid.size())) return 0;
        if (!(c >= 0 && c < grid[r].size())) return 0;
        if (grid[r][c] == '0') return 0;

        grid[r][c] = '0';

        solve(grid, r, c-1);
        solve(grid, r, c+1);
        solve(grid, r-1, c);
        solve(grid, r+1, c);

        return 1;
    }
    
    int numIslands(vector<vector<char>>& grid) {
        int res = 0;
        for (int i = 0; i < grid.size(); i++) {
            for (int j = 0; j < grid[i].size(); j++) {
                res += solve(grid, i, j);
            }
        }
        return res;
    }
};