题目链接：http://codeforces.com/contest/219/problem/D
树dp
1 //#pragma comment(linker, "/STACK:102400000, 102400000") 2 #include <algorithm> 3 #include <iostream> 4 #include <cstdlib> 5 #include <cstring> 6 #include <cstdio> 7 #include <vector> 8 #include <cmath> 9 #include <ctime> 10 #include <list> 11 #include <set> 12 #include <map> 13 using namespace std; 14 typedef long long LL; 15 typedef pair <int, int> P; 16 const int N = 2e5 + 5; 17 struct Edge { 18 int next, to, cost; 19 }edge[N << 1]; 20 int head[N], tot, d[N], ans1[N], ans[N]; 21 int res[N]; 22 23 inline void add_edge(int u, int v, int c) { 24 edge[tot].next = head[u]; 25 edge[tot].to = v; 26 edge[tot].cost = c; 27 head[u] = tot++; 28 } 29 30 void dfs1(int u, int p) { 31 d[u] = 1; 32 ans1[u] = 0; 33 for(int i = head[u]; ~i; i = edge[i].next) { 34 int v = edge[i].to; 35 if(v == p) 36 continue; 37 dfs1(v, u); 38 d[u] += d[v]; 39 ans1[u] += edge[i].cost + ans1[v]; 40 } 41 } 42 43 void dfs2(int u, int p) { 44 ans[u] += ans1[u]; 45 for(int i = head[u]; ~i; i = edge[i].next) { 46 int v = edge[i].to; 47 if(v == p) 48 continue; 49 ans[v] = ans[u] - ans1[v] - edge[i].cost + !edge[i].cost; 50 dfs2(v, u); 51 } 52 } 53 54 int main() 55 { 56 memset(head, -1, sizeof(head)); 57 int n, u, v; 58 scanf("%d", &n); 59 for(int i = 1; i < n; ++i) { 60 scanf("%d %d", &u, &v); 61 add_edge(u, v, 0); 62 add_edge(v, u, 1); 63 } 64 dfs1(1, -1); 65 dfs2(1, -1); 66 int Min = N, cnt = 0; 67 for(int i = 1; i <= n; ++i) { 68 Min = min(Min, ans[i]); 69 } 70 for(int i = 1; i <= n; ++i) { 71 if(ans[i] == Min) { 72 res[++cnt] = i; 73 } 74 } 75 printf("%d ", Min); 76 sort(res + 1, res + cnt + 1); 77 for(int i = 1; i <= cnt; ++i) { 78 printf("%d%c", res[i], i == cnt ? ' ': ' '); 79 } 80 return 0; 81 }