[USACO5.2]Snail Trails

嘟嘟嘟

一道很水的爆搜题，然后我调了近40分钟……

错误：输入数据最好用cin，因为数字可能不止一位，所以用scanf后，单纯的c[0]为字母，c[1]数字…………………………

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cctype>
 #include<vector>
 #include<stack>
 #include<queue>
 using namespace std;
 #define enter puts("")
 #define space putchar(' ')
 #define Mem(a, x) memset(a, x, sizeof(a))
 #define rg register
 typedef long long ll;
 typedef double db;
 const int INF = 0x3f3f3f3f;
 const db eps = 1e-;
 const int maxn = ;
 inline ll read()
 {
   ll ans = ;
   char ch = getchar(), last = ' ';
   while(!isdigit(ch)) {last = ch; ch = getchar();}
   while(isdigit(ch)) {ans = (ans << ) + (ans << ) + ch - ''; ch = getchar();}
   if(last == '-') ans = -ans;
   return ans;
 }
 inline void write(ll x)
 {
   if(x < ) x = -x, putchar('-');
   if(x >= ) write(x / );
   putchar(x %  + '');
 }

 int n, m, a[maxn][maxn];
 char c;
 int v;

 const int dx[] = {, , , -}, dy[] = {, , -, };
 int ans = ;
 void dfs(int x, int y, int step, int dir)
 {
   //printf("!%d %d\n", x, y);
   if(step > ans) ans = step;
   if(a[x + dx[dir]][y + dy[dir]] == )
     {
       a[x][y] = ;
       dfs(x + dx[dir], y + dy[dir], step + , dir);
       a[x][y] = ;
     }
   else if(!a[x + dx[dir]][y + dy[dir]])
     {
       for(int i = ; i < ; ++i)
     if(a[x + dx[i]][y + dy[i]] ==  && ((i + dir) & ))
       {
         a[x][y] = ;
         dfs(x + dx[i], y + dy[i], step + , i);
         a[x][y] = ;
       }
     }
 }

 int main()
 {
   n = read(); m = read();
   for(int i = ; i <= m; ++i)
     {
       cin >> c >> v;
       a[c - 'A' + ][v] = ;
     }
   for(int i = ; i <= n; ++i)
     for(int j = ; j <= n; ++j) a[i][j] ^= ;
   dfs(, , , ); dfs(, , , );
   write(ans), enter;
   return ;
 }