洛谷p1162 bfs

#include <iostream>
#include <queue>

using namespace std;

int map[40][40] = {0};//0代表未染色，1代表染色了，3代表邊界外染色
int n;

struct node {
	int x;
	int y;
}n1;

queue<node> q;

void bfs(int x,int y) {
	n1.x = x;
	n1.y = y;
	q.push(n1);
	map[x][y] = 3;//開始第一個位置染上顏色
	//
	
	while (!q.empty()) {
		int temp_x, temp_y;
		temp_x = q.front().x;
		temp_y = q.front().y;
		q.pop();
		if (temp_x - 1 > 0&& map[temp_x - 1][temp_y] == 0) {
			n1.x = temp_x - 1;
			n1.y = temp_y;
			map[temp_x - 1][temp_y] = 3;
			q.push(n1);
		}
		if (temp_x + 1 < n+2 && map[temp_x + 1][temp_y] == 0) {
			n1.x = temp_x + 1;
			n1.y = temp_y;
			map[temp_x + 1][temp_y] = 3;
			q.push(n1);
			
		}
		if (temp_y - 1 > 0 && map[temp_x][temp_y - 1] == 0) {
			n1.x = temp_x;
			n1.y = temp_y - 1;
			map[temp_x][temp_y - 1] = 3;
			q.push(n1);
		}
		if (temp_y + 1 < n + 2 && map[temp_x][temp_y + 1] == 0) {
			n1.x = temp_x;
			n1.y = temp_y + 1;
			map[temp_x][temp_y + 1] = 3;
			q.push(n1);
		}
	}

}

int main() {
	
	cin >> n;
	int temp;
	for (int  i = 1; i < n+1; i++)
	{
		
		for (int j = 1; j < n+1; j++)
		{
			cin >> temp;
			map[i][j] = temp;
		}
	}
	bfs(0, 0);
	for (int i = 1; i < n + 1; i++)
	{

		for (int j = 1; j < n + 1; j++)
		{
			if (map[i][j] == 3) {
				map[i][j] = 0;
			}
			else if (map[i][j]==0) {
				map[i][j] = 2;
			}
			cout << map[i][j] << " ";
		}
		cout << endl;
	}
	return 0;
}

精妙之處，我在原圖的外層加了一圈0，使得我的bfs能夠直接最終將邊界外的0全部染上。