Find the smallest ring Luo Gu P2661

Topic links: https://www.luogu.org/problem/P2661

Meaning of the questions: Everyone has a passing objects, at the beginning of each people only know their birthday, every one will know his own birthday told to pass an object, when his birthday hear from others at the end of the game, to inquire you can at least play a few rounds the game.

Analysis: is to find the smallest ring, dfs do, two arrays vis mark (code to a record as used), used an array of belonging vis conventional array, labeling this point has been visited, do not go, vis array is to find the smallest ring, arranged in no time lookup. Specific look at the code

#include <bits / STDC ++ H.>
 the using  namespace STD; 
typedef Long  Long LL;
 const  int MAXN = 2E5 + . 7 ;
 const  int N = MAXN * 20 is ;
 const LL INF = 0x3f3f3f3f ;
 #define MEM0 (A) Memset (A, 0 , the sizeof (a))
 int D [MAXN];
 int ANS = INF;
 int STEP [MAXN]; // for recording the number of sides passes through a first point in a loop 
int VIS [MAXN], used [MAXN]; // VIS recording array has passed this point lookup (used to determine whether the ring), used to mark the point used array has gone through once, do not go any farther 
void DFS ( intNd, int NUM) { // Nd, NUM respectively to the current node and the number of steps walked 
    IF (Used [Nd]) return ;
     IF (VIS [Nd]) { 
        ANS = min (ANS, num- STEP [Nd]); 
    } 
    the else { 
        VIS [Nd] = . 1 ; 
        STEP [Nd] = NUM; 
        DFS (D [Nd], NUM + . 1 ); 
        Used [Nd] = . 1 ; 
    } 
} 
int main () {
     int n- ; Scanf ( " % D " , & n-);
     for (int i=1;i<=n;i++){
        scanf("%d",&d[i]);
    }
    for(int i=1;i<=n;i++){
        dfs(i,0);
    }
    cout<<ans<<endl;
    return 0;
}