题目链接：https://ac.nowcoder.com/acm/contest/1870/J
题目大意：求最大的连通块是多大
主要是为了防止自己忘记bfs怎么写。。。。。
1 #include<stdio.h> 2 #include<string.h> 3 #include<queue> 4 #include<algorithm> 5 using namespace std; 6 const int MAXN = 800; 7 8 int l, h, vis[MAXN][MAXN]; 9 char map[MAXN][MAXN]; 10 int dx[8] = {0, 0, 1, 1, 1, -1, -1, -1}; //方向数组 11 int dy[8] = {1, -1, 1, 0, -1, 1, 0, -1}; 12 13 14 struct Node 15 { 16 int x, y; 17 }; 18 19 int check(int x, int y) 20 { 21 if(x < 1 || x > h || y < 1 || y > l) //不越界 22 return 0; 23 if(map[x][y] != '.') //不可走 24 return 0; 25 if(vis[x][y] == 1) //已经走过 26 return 0; 27 return 1; 28 } 29 30 int bfs(int x, int y) 31 { 32 int sum = 0; 33 queue<Node> Q; 34 while(!Q.empty()) Q.pop(); 35 Node no; 36 no.x = x, no.y = y; 37 vis[x][y] = 1; 38 sum ++; 39 Q.push(no); 40 while(!Q.empty()) 41 { 42 Node a = Q.front(); 43 Q.pop(); 44 for(int k = 0; k < 8; k ++) 45 { 46 Node next = a; 47 next.x += dx[k]; 48 next.y += dy[k]; 49 if(check(next.x, next.y)) 50 { 51 sum ++; 52 vis[next.x][next.y] = 1; 53 Q.push(next); 54 } 55 } 56 } 57 return sum; 58 } 59 60 int main() 61 { 62 int ans = -1; 63 scanf("%d%d", &l, &h); 64 getchar(); 65 for(int i = 1; i <= h; i ++) 66 scanf("%s", map[i] + 1); 67 for(int i = 1; i <= h; i ++) 68 for(int j = 1; j <= l; j ++) 69 if(!vis[i][j] && map[i][j] == '.') //进入bfs的条件 70 ans = max(ans, bfs(i, j)); 71 printf("%d ", ans); 72 return 0; 73 }