[POI2008]STA-Station

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cmath>
 4 #include<algorithm>
 5 #include<cstring>
 6 #include<cstdlib>
 7 #include<cctype>
 8 #include<vector>
 9 #include<stack>
10 #include<queue>
11 using namespace std;
12 #define enter puts("") 
13 #define space putchar(‘ ‘)
14 #define Mem(a, x) memset(a, x, sizeof(a))
15 #define rg register
16 typedef long long ll;
17 typedef double db;
18 const int INF = 0x3f3f3f3f;
19 const db eps = 1e-8;
20 const int maxn = 1e6 + 5;
21 inline ll read()
22 {
23     ll ans = 0;
24     char ch = getchar(), last = ‘ ‘;
25     while(!isdigit(ch)) {last = ch; ch = getchar();}
26     while(isdigit(ch)) {ans = ans * 10 + ch - ‘0‘; ch = getchar();}
27     if(last == ‘-‘) ans = -ans;
28     return ans;
29 }
30 inline void write(ll x)
31 {
32     if(x < 0) x = -x, putchar(‘-‘);
33     if(x >= 10) write(x / 10);
34     putchar(x % 10 + ‘0‘);
35 }
36 
37 int n, ans = 1;
38 struct Edge
39 {
40     int nxt, to;
41 }e[maxn << 1];
42 int head[maxn], ecnt = 0;
43 void addEdge(int x, int y)
44 {
45     e[++ecnt] = (Edge){head[x], y};
46     head[x] = ecnt;
47 }
48 
49 int siz[maxn], dep[maxn];
50 ll dp[maxn];
51 void dfs1(int now, int f)
52 {
53     siz[now] = 1;
54     for(int i = head[now]; i; i = e[i].nxt)
55     {
56         if(e[i].to == f) continue;
57         dep[e[i].to] = dep[now] + 1;
58         dp[1] += dep[e[i].to];
59         dfs1(e[i].to, now);
60         siz[now] += siz[e[i].to];
61     }
62     
63 }
64 void dfs2(int now, int f)
65 {
66     for(int i = head[now]; i; i = e[i].nxt)
67     {
68         if(e[i].to == f) continue;
69         dp[e[i].to] = dp[now] + n - (siz[e[i].to] << 1);
70         if(dp[e[i].to] > dp[ans]) ans = e[i].to;
71         dfs2(e[i].to, now);
72     }
73 }
74 
75 int main()
76 {
77     n = read();
78     for(int i = 1; i < n; ++i)
79     {
80         int x = read(), y = read();
81         addEdge(x, y); addEdge(y, x);
82     }
83     dfs1(1, 0); dfs2(1, 0);
84     write(ans); enter;
85     return 0;
86 }