Challenge: Count the Islands

Lab C++ Intermediate 20 points

In a map of # (land) and . (water), land cells touching up/down/left/right form one island. Print the number of islands and the size of the biggest (0 if there's no land).

Input

Line 1: rows cols. Then rows lines of # and ..

Output

Islands: <count>
Biggest: <size>

Example

Input

4 5
##..#
#...#
..#..
.....

Output

Islands: 3
Biggest: 3

Sample input available Sample output available

Editor

C++

Hints

Each # you haven't visited starts an island.

Flood-fill it with BFS, counting cells and turning them into water.

Solution explanation

Every cell is processed at most once: O(rows × cols).

Show solution

#include <algorithm>
#include <iostream>
#include <queue>
#include <string>
#include <vector>
using namespace std;

int main() {
    int R, C;
    cin >> R >> C;
    vector<string> g(R);
    for (auto& row : g) cin >> row;
    int count = 0, biggest = 0;
    int dr[] = {1, -1, 0, 0}, dc[] = {0, 0, 1, -1};
    for (int r = 0; r < R; r++)
        for (int c = 0; c < C; c++) {
            if (g[r][c] != '#') continue;
            count++;
            int size = 0;
            queue<pair<int, int>> q;
            q.push({r, c});
            g[r][c] = '.';
            while (!q.empty()) {
                auto [y, x] = q.front();
                q.pop();
                size++;
                for (int d = 0; d < 4; d++) {
                    int ny = y + dr[d], nx = x + dc[d];
                    if (ny >= 0 && ny < R && nx >= 0 && nx < C && g[ny][nx] == '#') {
                        g[ny][nx] = '.';
                        q.push({ny, nx});
                    }
                }
            }
            biggest = max(biggest, size);
        }
    cout << "Islands: " << count << endl;
    cout << "Biggest: " << biggest << endl;
    return 0;
}

Output

Answer