[BFS] [NYNUOJ] 1154 找食物

经典的BFS路长为一求最短路

思路:

先找钥匙 再找箱子

两次BFS 

未找到钥匙不可走箱子

先把箱子变墙

找到钥匙再恢复

注意判重

//#pragma GCC optimize(2)
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <string>
#include <cstring>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <vector>
#include <fstream>
#include <list>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;
 
const int MAXN = 1010;
 
char arr[1010][1010];

int usea[MAXN][MAXN] = {0}, useb[MAXN][MAXN] = {0};

ll n, m, ra, rb, ansa = 0, ansb = 0 , ta, tb;

bool finda = false, findb = false;
 
struct node
{
    int x, y, step;
 
    node(int xa, int ya, int za)
    {
        x = xa;
        y = ya;
        step = za;
    }   
};
 
int movel[4][2] = { {1, 0}, {0, 1}, {-1, 0}, {0, -1} };
 
queue <node> Q;

queue <node> QB;
 
void bfs(node a)
{
    Q.push(a);
 
    while(!Q.empty())
    {
        node b = Q.front();
 
        Q.pop();
 
        if( !(b.x < 1 || b.x > n || b.y < 1 || b.y > m || arr[b.x][b.y] == '*' || usea[b.x][b.y] == 1) )
        {
        	usea[b.x][b.y] = 1;
        	
            if(arr[b.x][b.y] == 'S')
            {
                finda = true;

                ansa = b.step;

                return ;
            }
            
            for(int i = 0; i < 4; i++)
            {
                
                Q.push(node(b.x + movel[i][0], b.y + movel[i][1], b.step + 1));
            }
        }
    }
}

void bfsb(node a)
{
	
    QB.push(a);
 
    while(!QB.empty())
    {
        node b = QB.front();
 
        QB.pop();
 
        if( !(b.x < 1 || b.x > n || b.y < 1 || b.y > m || arr[b.x][b.y] == '*' || useb[b.x][b.y] == 1) )
        {
        	useb[b.x][b.y] = 1;
            
			if(arr[b.x][b.y] == 'T')
            {
                findb = true;

                ansb = b.step;

                return ;
            }
            
            for(int i = 0; i < 4; i++)
            {
                
                QB.push(node(b.x + movel[i][0], b.y + movel[i][1], b.step + 1));
            }
        }
    }
}

int main()
{
    ios::sync_with_stdio(false);
 
    cin.tie(0);     cout.tie(0);
 
    cin>>n>>m;
    
    for(int i = 1; i <= n; i++)
    {
        for(int j = 1; j <= m; j++)
        {
            cin>>arr[i][j];

            if(arr[i][j] == 'T')
            {
                arr[i][j] = '*';

                ra = i;
                rb = j;
            }

            if(arr[i][j] == 'S')
            {
                ta = i;
                tb = j;
            }
        }
    }
 
    int x, y;
 
    cin>>x>>y;
 
    node in(x, y, 0);
    
    bfs(in);
 
    arr[ra][rb] = 'T';

    if(finda)
    {
        node in(ta, tb, 0);

        bfsb(in);
    }
    
    if(finda && findb)
        cout<<ansa + ansb<<endl;

    else
        cout<<"-1"<<endl;
 
 
    return 0;
}