【搜索】DFS与BFS

99. 岛屿数量

讲解：https://programmercarl.com/kamacoder/0099.岛屿的数量广搜.html#思路
DFS代码

#include <iostream>
#include <cstring>using namespace std;const int N = 55;int n, m;
int g[N][N];
bool st[N][N];
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};void dfs(int sx, int sy)
{for (int i = 0; i < 4; i++){int a = sx + dx[i], b = sy + dy[i];if (a < 0 || a >= n || b < 0 || b >= m) continue;if (st[a][b] || g[a][b] == 0) continue;st[a][b] = true;dfs(a, b);}
}int main()
{cin >> n >> m;for (int i = 0; i < n; i++)for (int j = 0; j < m; j++)cin >> g[i][j];int res = 0;for (int i = 0; i < n; i++){for (int j = 0; j < m; j++){if (!st[i][j] && g[i][j] == 1){st[i][j] = true;res++;dfs(i, j);}}}cout << res << endl;return 0;
}

BFS代码

#include <iostream>
#include <cstring>
#include <queue>using namespace std;typedef pair<int, int> PII;const int N = 55;int n, m;
int g[N][N];
bool st[N][N];
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};void bfs(int sx, int sy)
{queue<PII> q;q.push({sx, sy});st[sx][sy] = true;while (q.size()){PII t = q.front();q.pop();for (int i = 0; i < 4; i++){int a = t.first + dx[i], b = t.second + dy[i];if (a < 0 || a >= n || b < 0 || b >= m) continue;if (st[a][b] || g[a][b] == 0) continue;q.push({a, b});st[a][b] = true;}}
}int main()
{cin >> n >> m;for (int i = 0; i < n; i++)for (int j = 0; j < m; j++)cin >> g[i][j];int res = 0;for (int i = 0; i < n; i++){for (int j = 0; j < m; j++){if (!st[i][j] && g[i][j] == 1){res++;bfs(i, j);}}}cout << res << endl;return 0;
}