牛客多校补题3

J

思路

模拟+搜索，比赛的时候就一个细节写错了

#include <bits/stdc++.h>
#define int long long
#define endl '\n'
using namespace std;
const int N = 5e5 + 10, mod = 1e9 + 7, INF = 0x3f3f3f3f3f3f3f3f;
int h[5*N], e[20 * N], ne[20 * N], idx;
int dist[5*N];
int a[N][5];
int n;
int s1, s2, t1, t2;
void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
struct node
{
    int x, y, z;
};
void bfs()
{
    map<pair<int, int>, int> mp;
    deque<node> dq;
    dq.push_back({s1, s2, 0});
    while (dq.size())
    {
        auto it = dq.front();
        dq.pop_front();
        int x = it.x, y = it.y, z = it.z;
        if (x == t1 && y == t2)
        {
            cout << z;
            return;
        }
        if(mp[{x,y}])continue;
        mp[{x, y}] = 1;
        for (int j = 1; j <= 4; j++)
        {
            int p = a[y][j];
            int w = j % 4 + 1;
            if (p == x)
            {
                if (mp[{y, a[y][w]}] || a[y][w] == 0)
                    continue;
                dq.push_front({y, a[y][w], z});
               
            }
            else
            {
                if (mp[{y, a[y][w]}] || a[y][w] == 0)
                    continue;
                dq.push_back({y, a[y][w], z + 1});
            }
        }
    }
    cout << -1 << endl;
}
signed main()
{
    ios::sync_with_stdio(false), cin.tie(nullptr);
    memset(h, -1, sizeof h);
    cin >> n;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= 4; j++)
        {
            cin >> a[i][j];
            if (!a[i][j])
                continue;
            add(i, a[i][j]);
            add(a[i][j], i);
        }
    cin >> s1 >> s2 >> t1 >> t2;
    bfs();
    return 0;
}