Igor In the Museum CodeForces - 598D

本文介绍了一个基于图遍历算法的游戏场景模拟问题。主人公伊戈尔身处一个由空地和墙壁组成的矩形博物馆中,需要从指定起点出发,在不离开博物馆边界的前提下尽可能多地欣赏到墙上的画作。通过深度优先搜索策略计算不同起点所能达到的最大观画数量。

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Igor is in the museum and he wants to see as many pictures as possible.

Museum can be represented as a rectangular field of n × m cells. Each cell is either empty or impassable. Empty cells are marked with '.', impassable cells are marked with '*'. Every two adjacent cells of different types (one empty and one impassable) are divided by a wall containing one picture.

At the beginning Igor is in some empty cell. At every moment he can move to any empty cell that share a side with the current one.

For several starting positions you should calculate the maximum number of pictures that Igor can see. Igor is able to see the picture only if he is in the cell adjacent to the wall with this picture. Igor have a lot of time, so he will examine every picture he can see.

Input

First line of the input contains three integers n, m and k (3 ≤ n, m ≤ 1000, 1 ≤ k ≤ min(n·m, 100 000)) — the museum dimensions and the number of starting positions to process.

Each of the next n lines contains m symbols '.', '*' — the description of the museum. It is guaranteed that all border cells are impassable, so Igor can't go out from the museum.

Each of the last k lines contains two integers x and y (1 ≤ x ≤ n, 1 ≤ y ≤ m) — the row and the column of one of Igor's starting positions respectively. Rows are numbered from top to bottom, columns — from left to right. It is guaranteed that all starting positions are empty cells.

Output

Print k integers — the maximum number of pictures, that Igor can see if he starts in corresponding position.

Example
Input
5 6 3
******
*..*.*
******
*....*
******
2 2
2 5
4 3
Output
6
4
10
Input
4 4 1
****
*..*
*.**
****
3 2
Output
8

题意:

“.”代表空地,“*”代表墙壁,墙壁上挂有画,从给定位置走遍所有能到达的空地

求能看最多画作的数量

思路:相邻的空地可以看到的画作数量相等

#include<stdio.h>
#include<string.h>
using namespace std;
const int N = 1005;
int n,m;
char mp[N][N];
int vis[N][N],t[N][N];
int next[4][2]={1,0,-1,0,0,1,0,-1};
int time,ans;
int arr[N*N];
void Getmap(){
	for(int i=0;i<n;i++)
	  scanf("%s",mp[i]);
}
int check(int x,int y){
	if(x<0||y<0||x>=n||y>=m) return 1;
	return 0;
}
void Dfs(int x,int y){
	vis[x][y]=1;
	t[x][y]=time;
	for(int i=0;i<4;i++){
		int tx=x+next[i][0];
		int ty=y+next[i][1];
		if(check(tx,ty)||vis[tx][ty]) continue;
		if(mp[tx][ty]=='*') ans++;
		else Dfs(tx,ty);
	}
}
int main(){
	int T;
	scanf("%d%d%d",&n,&m,&T);
	Getmap();
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++){
			if(mp[i][j]=='.'&&!vis[i][j]){
				time++;
				ans=0;
				Dfs(i,j);
				arr[time]=ans;
			} 
		}
	}
	while(T--){
		int x,y;
		scanf("%d%d",&x,&y);
		printf("%d\n",arr[t[x-1][y-1]]);
	}
	return 0;
}

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