https://ac.nowcoder.com/acm/contest/331/I

C++版本一

std

题解：

注意到固定转向的镜子没有办法汇聚，也就没有办法卡掉模拟光线。

直接模拟即可，或者使用并查集或者记忆化搜索也可。

时间复杂度O(NM)

#include <bits/stdc++.h>
 
using namespace std;
 
//为了更好的扩展性，这里提供一份记忆化搜索题解
 
const int mn = 505;
 
int n, m;
char s[mn][mn];
 
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, 1, -1};
 
int d[mn][mn][4];  // up down left right
 
int dp(int x, int y, int from) {
    int &ans = d[x][y][from];
    if (ans) return ans;
    if (x == n + 1) return y;
    if (y <= 0 || y > m || x <= 0) return -1;
    if (s[x][y] == '\\') {
        if (from == 0) ans = dp(x, y + 1, 2);
        if (from == 1) ans = dp(x, y - 1, 3);
        if (from == 2) ans = dp(x + 1, y, 0);
        if (from == 3) ans = dp(x - 1, y, 1);
    }
    if (s[x][y] == '/') {
        if (from == 0) ans = dp(x, y - 1, 3);
        if (from == 1) ans = dp(x, y + 1, 2);
        if (from == 2) ans = dp(x - 1, y, 1);
        if (from == 3) ans = dp(x + 1, y, 0);
    }
    if (s[x][y] == '.') ans = dp(x + dx[from], y + dy[from], from);
    return ans;
}
 
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i++) scanf("%s", s[i] + 1);
    for (int i = 1; i <= m; i++) printf("%d\n", dp(1, i, 0));
    return 0;
}

C++版本二

DFS

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=500+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
int ans,cnt,flag,temp;
int dir[][2]={-1,0,0,1,1,0,0,-1};
char str[N][N];

int find(int flag,int x,int y,int c){
    cout<<x<<" "<<y<<endl;
    if(x<1||y<1||y>m)
        return -1;
    if(x>n)
        return y;
    if(c>n*m)
        return -1;
    if(str[x][y]=='\\'){
        if(flag==0)
            flag=3;
        else if(flag==1)
            flag=2;
        else if(flag==2)
            flag=1;
        else if(flag==3)
            flag=0;
    }
    if(str[x][y]=='/'){
        if(flag==0)
            flag=1;
        else if(flag==1)
            flag=0;
        else if(flag==2)
            flag=3;
        else if(flag==3)
            flag=2;
    }
    return find(flag,x+dir[flag][0],y+dir[flag][1],c+1);
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    scanf("%d%d",&n,&m);
    //scanf("%d",&t);
    //while(t--){}
    for(int i=1;i<=n;i++)
        scanf("%s",str[i]+1);
    for(int i=1;i<=m;i++)
        cout << find(2,1,i,1) << endl;
    //cout << "Hello world!" << endl;
    return 0;
}