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("
"))
		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
", ans);
	return 0;
}