POJ 1655 - Balancing Act

 1 // poj1655 Balancing Act
 2 #include <iostream>
 3 #include <cstring>
 4 #define NDEBUG
 5 
 6 #ifndef NDEBUG
 7 #include <cstdio>
 8 #endif
 9 
10 #define MAXN    20005
11 
12 using namespace std;
13 
14 int N;
15 int edgefw[MAXN*2], edge[MAXN*2], head[MAXN], eptr;
16 
17 #define EI(j, k)    ({ 18     edge[eptr] = k, edgefw[eptr] = head[j];    19     head[j] = eptr++;    20 })
21 
22 int dp[MAXN], dp2[MAXN];
23 char vis[MAXN];
24 
25 void dfs(int i)
26 {
27     vis[i] = 1;
28     int p, maxk = 0, sumn = 1;
29     for(p = head[i]; p>=0; p = edgefw[p]) {
30         int t = edge[p];
31         if (!vis[t]) {
32             if (!dp2[t]) dfs(t);
33             sumn += dp2[t];
34             if (maxk < dp2[t])
35                     maxk = dp2[t];
36         }
37     }
38     if (sumn != N && N - sumn > maxk) maxk = N - sumn;
39     dp[i] = maxk, dp2[i] = sumn;
40 }
41 
42 int main(void)
43 {
44     #ifndef NDEBUG
45     freopen("poj1655.in", "r", stdin);
46     #endif // NDEBUG
47     int T;
48     for(cin >> T; T; --T) {
49         cin >> N;
50         memset(vis, 0, sizeof(vis));
51         memset(dp2, 0, sizeof(dp2));
52         memset(head, -1, sizeof(head)), eptr = 0;
53         int i, j, root;
54         root = 0;
55         for(i=0; i<N-1; ++i) {
56             int k;
57             cin >> j >> k;
58             --j,--k; EI(j, k), EI(k, j);
59             if (root == k) root = j;
60         }
61         dfs(root);
62         j = 0;
63         for(i = 1; i < N; ++i)
64             if (dp[i] < dp[j])
65                 j = i;
66         cout << j+1 << ‘ ‘ << dp[j] << endl;
67     }
68     return 0;
69 }