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…………………………
1 #include<cstdio> 2 #include<iostream> 3 #include<cmath> 4 #include<algorithm> 5 #include<cstring> 6 #include<cstdlib> 7 #include<cctype> 8 #include<vector> 9 #include<stack> 10 #include<queue> 11 using namespace std; 12 #define enter puts("") 13 #define space putchar(' ') 14 #define Mem(a, x) memset(a, x, sizeof(a)) 15 #define rg register 16 typedef long long ll; 17 typedef double db; 18 const int INF = 0x3f3f3f3f; 19 const db eps = 1e-8; 20 const int maxn = 125; 21 inline ll read() 22 { 23 ll ans = 0; 24 char ch = getchar(), last = ' '; 25 while(!isdigit(ch)) {last = ch; ch = getchar();} 26 while(isdigit(ch)) {ans = (ans << 1) + (ans << 3) + ch - '0'; ch = getchar();} 27 if(last == '-') ans = -ans; 28 return ans; 29 } 30 inline void write(ll x) 31 { 32 if(x < 0) x = -x, putchar('-'); 33 if(x >= 10) write(x / 10); 34 putchar(x % 10 + '0'); 35 } 36 37 int n, m, a[maxn][maxn]; 38 char c; 39 int v; 40 41 const int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0}; 42 int ans = 0; 43 void dfs(int x, int y, int step, int dir) 44 { 45 //printf("!%d %d ", x, y); 46 if(step > ans) ans = step; 47 if(a[x + dx[dir]][y + dy[dir]] == 1) 48 { 49 a[x][y] = 2; 50 dfs(x + dx[dir], y + dy[dir], step + 1, dir); 51 a[x][y] = 1; 52 } 53 else if(!a[x + dx[dir]][y + dy[dir]]) 54 { 55 for(int i = 0; i < 4; ++i) 56 if(a[x + dx[i]][y + dy[i]] == 1 && ((i + dir) & 1)) 57 { 58 a[x][y] = 2; 59 dfs(x + dx[i], y + dy[i], step + 1, i); 60 a[x][y] = 1; 61 } 62 } 63 } 64 65 int main() 66 { 67 n = read(); m = read(); 68 for(int i = 1; i <= m; ++i) 69 { 70 cin >> c >> v; 71 a[c - 'A' + 1][v] = 1; 72 } 73 for(int i = 1; i <= n; ++i) 74 for(int j = 1; j <= n; ++j) a[i][j] ^= 1; 75 dfs(1, 1, 1, 0); dfs(1, 1, 1, 1); 76 write(ans), enter; 77 return 0; 78 }