200. Number of Islands (https://leetcode.com/problems/number-of-islands/)

number-of-islands.cpp

class Solution {
private:
    void eraseIsland(vector<vector<char>>& grid, int x, int y) {
        if (grid[y][x] == '0') {
            return;
        }
        grid[y][x] = '0';

        if (y > 0) eraseIsland(grid, x, y - 1);
        if (y < grid.size() - 1) eraseIsland(grid, x, y + 1);
        if (x > 0) eraseIsland(grid, x - 1, y);
        if (x < grid[0].size() - 1) eraseIsland(grid, x + 1, y);
    }
public:
    int numIslands(vector<vector<char>>& grid) {
        int islands = 0;

        for (int y = 0; y < grid.size(); y++) {
            for (int x = 0; x < grid[0].size(); x++) {
                if (grid[y][x] == '1') {
                    eraseIsland(grid, x, y);
                    islands++;
                }
            }
        }
        return islands;
    }
};