BFS寻求最短距离

题目：http://acm.swust.edu.cn/oj/problem/4/

这是一道简单的题目，但是可以说明问题了。

 

#include "iostream"
#include "string"
#include "cstdio"
#include "cstring"
#include "algorithm"
#include "queue"
using namespace std;
char Map[105][105];
int Used[105][105];
int Dir[4][2]={{0, 1}, {0, -1}, {-1, 0}, {1, 0}};
int T, N, M, i, j, k, si, sj;
struct Dot
{
    int x, y;
    int Step;
};

int BFS()
{
    Used[si][sj] = 1;
    Dot tmp;
    queue<Dot> Q;
    tmp.x = si;
    tmp.y = sj;
    tmp.Step = 0;
    Q.push(tmp);
    while(!Q.empty())
    {
        tmp = Q.front();
        Q.pop();
        for(i=0; i<4; i++)
        {
            Dot tmp2;
            tmp2.x = tmp.x+Dir[i][0];
            tmp2.y = tmp.y+Dir[i][1];
            if(tmp2.x>=0 && tmp2.x<N && tmp2.y>=0 && tmp2.y<M && Used[tmp2.x][tmp2.y]==0)
            {
                if(Map[tmp2.x][tmp2.y]=='-')
                {
                    tmp2.Step = tmp.Step+1;
                    Used[tmp2.x][tmp2.y]=1;
                    Q.push(tmp2);
                }
                else if(Map[tmp2.x][tmp2.y]=='E') return (tmp.Step+1);
            }
        }
    }
    return -1;
}

int main()
{
    cin>>T;
    while(T--)
    {
        cin>>N>>M;
        memset(Used, 0, sizeof(Used));
        for(i=0; i<N; i++)
            for(j=0; j<M; j++)
            {
                cin>>Map[i][j];
                if(Map[i][j]=='S')
                {
                    si = i;
                    sj = j;
                }
            }
        cout<<BFS()<<endl;
    }
}