Computer net

原题

照着PPT的思想做了第一道二次动规

#include <iostream>#include <algorithm>#define MAXN 10010using namespace std ;int pre[MAXN] , leaf[MAXN] , n , child[MAXN] , dis[MAXN][2] , m ;void Readin (){int i ;scanf ("%d" , &n) ;memset (pre , 0 , sizeof (pre)) ;memset (child , 0 , sizeof (child)) ;memset (dis , 0 , sizeof (dis)) ;for (i = 2 ; i <= n ; i ++){scanf ("%d" , &pre[i]) ;child[pre[i]] ++ ;}for (m = 0 , i = 1 ; i <= n ; i ++)if (!child[i])leaf[m ++] = i ;}void Comp (){int i , j , ans ;for (i = 0 ; pre[leaf[i]] ; i ++)//从叶子到根，不仅要记录最优值，还要记录次优值{j = leaf[i] ;if (dis[j][0] + 1 >= dis[pre[j]][0]){dis[pre[j]][1] = dis[pre[j]][0] ;dis[pre[j]][0] = dis[j][0] + 1 ;}else if (dis[j][0] + 1 > dis[pre[j]][1])dis[pre[j]][1] = dis[j][0] + 1 ;if (!(-- child[pre[j]]))leaf[m ++] = pre[j] ;}for (i = m - 2 ; i >= 0 ; i --)//从根到叶子{j = leaf[i] ;if (dis[j][0] + 1 == dis[pre[j]][0]){if (dis[pre[j]][1] + 1 >= dis[j][0])dis[j][1] = dis[j][0] , dis[j][0] = dis[pre[j]][1] + 1 ;else if (dis[pre[j]][1] + 1 > dis[j][1])dis[j][1] = dis[pre[j]][1] + 1;}elsedis[j][1] = max (dis[j][0] , dis[pre[j]][1] + 1) , dis[j][0] = dis[pre[j]][0] + 1;}for (ans = MAXN , i = 1 ; i <= n ; i ++)if (dis[i][0] < ans)ans = dis[i][0] ;for (i = 1 ; i <= n ; i ++)if (dis[i][0] == ans)printf ("%d " , i) ;}int main (){Readin () ;Comp () ;return 0 ;}