Link

http://codeforces.com/contest/996/problem/C

answer

My English is not good, I misunderstood the meaning of the question at first, so I wrote$3K$The code results in non-stop$WA$, I later learned that a kind of garage can only allow the corresponding cars to enter.
The correct solution is this, you let the car keep spinning, and if anyone arrives at their door, they go in.
The conditions for no solution are that there are no vacancies at the beginning and no car is in front of the house.
One of the things that is hard to debug here is when rotating, if you always use it mechanically it's the same every time$for$loop, then it is possible to make every time$0$all come back to the same place, I think I could write a piece of code that looks for each time$0$position, and then let it keep swapping positions with adjacent cars (along a fixed direction), and each time$0$The stop position is not the same as last time.
Think about it if$0$returns to the same position every time, then this$0$It is equivalent to occupying this position. If a car must enter the garage from this position, it will fall into an infinite loop.
I ended up using randomization and every move has$50\%$The probability of cancellation is guaranteed, so as to ensure that it will not be stuck by extreme data.
The above is an algorithm based on making all the cars turn around and then checking whether they can enter the garage. If you use every time you move a car to check whether it has come to your door, you don't need to consider the above problem

code

#include <cstdio>
#include <algorithm>
#include <cstdio>
#define maxn 100
#define rep(x) for(int i=1;i<=x;i++)
#define rd (rand()&1)
using namespace std;
int now[10][maxn], dx[maxn], dy[maxn], n, k, q[200010][3], head, tail, res;
void push(int a, int b, int c)
{
    q[tail][0]=a, q[tail][1]=b, q[tail][2]=c;
    tail++;
}
void up(int x, int y)
{
    push(now[x][y],x-1,y);
    swap(now[x][y],now[x-1][y]);
}
void down(int x, int y)
{
    push(now[x][y],x+1,y);
    swap(now[x][y],now[x+1][y]);
}
void left(int x, int y)
{
    push(now[x][y],x,y-1);
    swap(now[x][y],now[x][y-1]);
}
void right(int x, int y)
{
    push(now[x][y],x,y+1);
    swap(now[x][y],now[x][y+1]);
}
void park()
{
    int i, t;
    for(i=1;i<=n;i++)
    {
        t=now[2][i];
        if(i==dy[t] and dx[t]==1)up(2,i), res--;
    }
    for(i=1;i<=n;i++)
    {
        t=now[3][i];
        if(i==dy[t] and dx[t]==4)down(3,i), res--;
    }
}
void init()
{
    int i, j;
    scanf("%d%d",&n,&k);res=k;
    for(i=1;i<=4;i++)for(j=1;j<=n;j++)scanf("%d",now[i]+j);
    for(i=1;i<=4;i+=3)for(j=1;j<=n;j++)if(now[i][j])dx[now[i][j]]=i, dy[now[i][j]]=j, now[i][j]=0;
    park();
}
void spin()
{
    int i;
    for(i=n-1;i;i--)if(now[2][i] and now[2][i+1]==0 and rd)right(2,i);
    if(now[3][1] and now[2][1]==0 and rd)up(3,1);
    for(i=2;i<=n;i++)if(now[3][i] and now[3][i-1]==0 and rd)left(3,i);
    if(now[2][n] and now[3][n]==0 and rd)down(2,n);
}
void show()
{
    for(printf("%d\n",tail-head);head^tail;head++)printf("%d %d %d\n",q[head][0],q[head][1],q[head][2]);
}
int main()
{
    int i;
    init();
    for(i=1;i<=n;i++)if(now[2][i]==0 or now[3][i]==0)break;
    if(i>n){printf("-1");return 0;}
    while(res)spin(), park();
    show();
    return 0;
}