Codeforces round #516 (Div. 1, by Moscow team Olympus IAD) E

Question chain description

To assign a laser to a specified receiver and maximize the number, you only need to place a plane mirror at N * n positions.

Sol

We found that one row either put '/' or only '\', and answer = n | answer = n-1, which can be merged backwards.

Description

 

#include<bits/stdc++.h>#define N 1006using namespace std;int n,a[N],last;char ans[N][N];signed main () {    scanf("%d",&n);    for (int i=1;i<=n;i++) {     scanf("%d",a+i);      if (a[i]!=i) last=i; }    if (last) {        char x=‘/‘, y=‘\\‘;        for(int i=n;i;--i){            int p=0;            if(x==‘/‘){for(int j=1;j<last;++j) if(a[j]!=j){ p=j; break;} }            else for(int j=n;j>last;--j) if(a[j]!=j){ p=j; break;}            if(!p) break;            ans[i][p]=ans[i][last]=ans[i][a[p]]=x;            a[last]=a[a[p]], a[a[p]]=a[p], last=p;            swap(x,y);            cerr<<last<<endl;        }    }    printf("%d\n",n-(!!last));    for(int i=1; i<=n; ++i, puts("")) for(int j=1; j<=n; ++j) putchar(ans[i][j]?ans[i][j]:‘.‘);}

 

Codeforces round #516 (Div. 1, by Moscow team Olympus IAD) E