洛谷 P1560 [USACO5.2]蜗牛的旅行Snail Trails
题目链接
题解
一看题没什么思路。写了个暴力居然可过?!
Code
#include<bits/stdc++.h>
#define LL long long
#define RG register
using namespace std;
inline int gi() {
bool f = 0; char c = getchar();
RG int x = 0;
while (c!='-' && (c < '0' || c > '9')) c = getchar();
if (c == '-') f = 1, c = getchar();
while (c >= '0' && c <= '9') x = x*10+c-'0', c = getchar();
return f ? -x:x;
}
const int N = 210;
bool a[N][N], vis[N][N];
int mv[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}}, ans;
void dfs(int x, int y, int d, int z) {
int xx = x+mv[d][0], yy = y+mv[d][1];
if (vis[xx][yy]) {
ans = max(ans, z);
return ;
}
if (!a[xx][yy]) {
vis[xx][yy] = 1;
dfs(xx, yy, d, z+1);
vis[xx][yy] = 0;
}
else {
int dd = (d+1)%4;
bool flag = 0;
xx = x+mv[dd][0], yy = y+mv[dd][1];
if (!a[xx][yy] && !vis[xx][yy]) {
vis[xx][yy] = 1;
flag = 1, dfs(xx, yy, dd, z+1);
vis[xx][yy] = 0;
}
dd = (d+3)%4;
xx = x+mv[dd][0], yy = y+mv[dd][1];
if (!a[xx][yy] && !vis[xx][yy]) {
vis[xx][yy] = 1;
flag = 1, dfs(xx, yy, dd, z+1);
vis[xx][yy] = 0;
}
if (!flag) ans = max(ans, z);
}
return ;
}
int main() {
int n = gi(), ss = gi(), x;
char s;
for (int i = 1; i <= ss; i++) {
cin >> s >> x;
a[x][s-'A'+1] = 1;
}
for (int i = 1; i <= n; i++)
a[0][i] = a[i][0] = a[n+1][i] = a[i][n+1] = 1;
/* for (int i = 0; i <= n+1; i++, printf("\n"))
for (int j = 0; j <= n+1; j++)
printf("%d ", a[i][j]);*/
vis[1][1] = 1;
dfs(1, 1, 0, 1);
dfs(1, 1, 1, 1);
printf("%d\n", ans);
return 0;
}