P1560 学习笔记

省流：搜索水蓝。

题目传送门

拿到这个题目，第一眼就看到一个小玩意在网格中走，这不一眼 dfs 暴搜吗？

直接开搜。

code

/**********************************************************
 * Author        : dingziyang888
 * Website       : https://www.luogu.com.cn/problem/
 * Created Time  :
 * FileName      :
 * Warning!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 * 1.MLE?
 * 2.array size enough?
 * 3.long long?
 * 4.overflow long long?
 * 5.multiple task cleaned?
 * 6.freopen?
 * 7.TLE?
 * *******************************************************/
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <climits>
#include <stack>
#define I using
#define AK namespace
#define IOI std
#define A return
#define C 0
#define Ofile(s) freopen(s".in", "r", stdin), freopen (s".out", "w", stdout)
#define Cfile(s) fclose(stdin), fclose(stdout)
#define fast ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
I AK IOI;

using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
using lb = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;

constexpr int mod = 998244353;
constexpr int maxn = 2e2 + 5;

int ans, n, m, vv;
char c;

int dx[4] = {1, 0, -1, 0};// x轴偏移量
int dy[4] = {0, 1, 0, -1};// y轴偏移量
int vis[maxn][maxn], g[maxn][maxn];// vis 记录有没有走过，g 记录障碍物位置

stack<pair<int, int> > q;// 放栈里

void out(int xx, int yy) {
	int x = q.top().first, y = q.top().second;
	while (!q.empty() && x != xx || y != yy) 
		q.pop(), vis[x][y] = 0, x = q.top().first, y = q.top().second;
}//出栈

void dfs(int bx, int by, int sm, int dep) {
	int now = sm;
	for (int d = 0; d < 4; d++) {
		int x = bx + dx[d], y = by + dy[d];
		while (!g[x][y] && !vis[x][y] && x <= n && x > 0 && y <= n && y > 0) { // 是否为障碍物 && 有没有走过 && 有没有出网格
			q.push(make_pair(x, y));
			vis[x][y] = 1;
			now++;
			x = x + dx[d], y = y + dy[d];
		}
		x = x - dx[d], y = y - dy[d];
		if (x == bx && y == by)
			continue;
		ans = max(ans, now);// 更新 ans
		if (!vis[x + dx[d]][y + dy[d]])
			dfs(x, y, now, dep + 1);// 偏移量也没走过，直接搜
		now = sm;
		out(bx, by);
	}
}

int main() {
	freopen("std.in", "r", stdin);
	freopen("std.out", "w", stdout);
	cin >> n >> m;
	for (int i = 1; i <= m; i++)
		cin >> c >> vv, g[vv][c - 'A' + 1] = 1;
	q.push(make_pair(1, 1));//初始化
	vis[1][1] = 1;//初始化
	dfs(1, 1, 1, 1);
	cout << ans << endl;
	return 0;
}