[搜索]DFS+BFS

从一道水题 看下基本思路

POJ 3620  DFS ver1.

#include<iostream>
#include<queue>
using namespace std;

#define FRE freopen("in.txt","r",stdin)
const int N = 110;

int map[110][110];
int xmove[4][2] = {-1, 0, 1, 0, 0, -1, 0, 1};
int n, m;
int cnt, ans;
int  dfs(int x, int y)
{
	int i, Mx, My ,ans = 0;
	for(i=0;i<4;i++)
	{
		Mx = x + xmove[i][0];
		My = y + xmove[i][1];
		if(Mx<0||My<0||Mx==n||My==m||map[Mx][My]==0)
			continue;
		//printf("%d %d\n", Mx, My);
		map[Mx][My] = 0;
		ans += dfs(Mx, My) + 1;
	}
	return ans;
}
int main()
{
	//FRE;
	int k;
	scanf("%d%d%d", &n, &m, &k);
	int i, j,  x, y;
	memset(map, 0, N*N*sizeof(int));
	for(i=0;i<k;i++)
	{
		scanf("%d%d", &x, &y);
		map[x-1][y-1] = 1;
	}
	int res = 0;
	for(i=0;i<n;i++)
	{
		for(j=0;j<m;j++)
			if(map[i][j])
			{
				map[i][j] = 0;
				res = max(dfs(i, j)+1, res);
			}
	}
	printf("%d\n", res);
}

POJ 3620  DFS ver12

#include<iostream>
#include<queue>
using namespace std;

#define FRE freopen("in.txt","r",stdin)
const int N = 110;

int map[110][110];
int xmove[4][2] = {-1, 0, 1, 0, 0, -1, 0, 1};
int n, m;
int cnt, ans;
void dfs(int x, int y)
{
	int i, Mx, My;
	for(i=0;i<4;i++)
	{
		Mx = x + xmove[i][0];
		My = y + xmove[i][1];
		if(Mx<0||My<0||Mx==n||My==m||map[Mx][My]==0)
			continue;
		//printf("%d %d\n", Mx, My);
		map[Mx][My] = 0;
		cnt++;
		dfs(Mx, My);
	}
}
int main()
{
	//FRE;
	int k;
	scanf("%d%d%d", &n, &m, &k);
	int i, j,  x, y;
	memset(map, 0, N*N*sizeof(int));
	for(i=0;i<k;i++)
	{
		scanf("%d%d", &x, &y);
		map[x-1][y-1] = 1;
	}
	int res = 0;
	for(i=0;i<n;i++)
	{
		for(j=0;j<m;j++)
			if(map[i][j])
			{
				cnt = 1;
				map[i][j] = 0;
				dfs(i, j);
				res = max(res, cnt);
			}
	}
	printf("%d\n", res);
}

POJ 3626 BFS ver.

#include<iostream>
using namespace std;

#define FRE freopen("in.txt","r",stdin)
const int N = 1010;

int xmove[4][2] = {-1, 0, 1, 0, 0, -1, 0, 1};
int map[N][N];
int que[N*N][2];
int step[N][N];
int Dx, Dy;
int  bfs(int x, int y)
{
	int i, front = 0, rear = 0, ans = 0;
	int Mx, My;
	map[x][y] = 0;
	que[rear][0] = x;
	que[rear][1] = y;
	bool find = false;
	while(front<=rear&&!find)
	{
		for(i=0;i<4;i++)
		{
			Mx = que[front][0] + xmove[i][0];
			My = que[front][1] + xmove[i][1];
			//printf("%d %d %d\n", Mx, My);
			if(Mx<0||My<0||Mx>1000||My>1000||map[Mx][My])
				continue;
			step[Mx][My] = step[que[front][0]][que[front][1]] + 1;
			if(Mx==Dx&&My==Dy)
			{
				ans = step[Mx][My];
				find = true;
			}
			map[Mx][My] = 1;
			//printf("%d %d\n", Mx, My);
			rear++;
			que[rear][0] = Mx;
			que[rear][1] = My;
		}
		front++;
		//printf("queue:%d %d\n", front, rear);
	}
	return ans;
}
int main()
{
	//FRE;
	int k;
	scanf("%d%d%d", &Dx, &Dy, &k);
	Dx += 500;
	Dy += 500;
	int i, j;
	memset(map, 0, N*N*sizeof(int));
	int x, y;
	for(i=0;i<k;i++)
	{
		scanf("%d%d", &x, &y);
		map[x+500][y+500] = 1;
	}
	printf("%d\n", bfs(500, 500));
}