题目链接：http://hihocoder.com/problemset/problem/1050
整理个板子
1 /* 2 ━━━━━┒ギリギリ♂ eye！ 3 ┓┏┓┏┓┃キリキリ♂ mind！ 4 ┛┗┛┗┛┃＼○／ 5 ┓┏┓┏┓┃ / 6 ┛┗┛┗┛┃ノ) 7 ┓┏┓┏┓┃ 8 ┛┗┛┗┛┃ 9 ┓┏┓┏┓┃ 10 ┛┗┛┗┛┃ 11 ┓┏┓┏┓┃ 12 ┛┗┛┗┛┃ 13 ┓┏┓┏┓┃ 14 ┃┃┃┃┃┃ 15 ┻┻┻┻┻┻ 16 */ 17 #include <algorithm> 18 #include <iostream> 19 #include <iomanip> 20 #include <cstring> 21 #include <climits> 22 #include <complex> 23 #include <fstream> 24 #include <cassert> 25 #include <cstdio> 26 #include <bitset> 27 #include <vector> 28 #include <deque> 29 #include <queue> 30 #include <stack> 31 #include <ctime> 32 #include <set> 33 #include <map> 34 #include <cmath> 35 using namespace std; 36 #define fr first 37 #define sc second 38 #define cl clear 39 #define BUG puts("here!!!") 40 #define W(a) while(a--) 41 #define pb(a) push_back(a) 42 #define Rint(a) scanf("%d", &a) 43 #define Rll(a) scanf("%I64d", &a) 44 #define Rs(a) scanf("%s", a) 45 #define Cin(a) cin >> a 46 #define FRead() freopen("in", "r", stdin) 47 #define FWrite() freopen("out", "w", stdout) 48 #define Rep(i, len) for(int i = 0; i < (len); i++) 49 #define For(i, a, len) for(int i = (a); i < (len); i++) 50 #define Cls(a) memset((a), 0, sizeof(a)) 51 #define Clr(a, x) memset((a), (x), sizeof(a)) 52 #define Full(a) memset((a), 0x7f7f7f, sizeof(a)) 53 #define lrt rt << 1 54 #define rrt rt << 1 | 1 55 #define pi 3.14159265359 56 #define RT return 57 #define lowbit(x) x & (-x) 58 #define onecnt(x) __builtin_popcount(x) 59 typedef long long LL; 60 typedef long double LD; 61 typedef unsigned long long ULL; 62 typedef pair<int, int> pii; 63 typedef pair<string, int> psi; 64 typedef pair<LL, LL> pll; 65 typedef map<string, int> msi; 66 typedef vector<int> vi; 67 typedef vector<LL> vl; 68 typedef vector<vl> vvl; 69 typedef vector<bool> vb; 70 71 typedef struct Edge { 72 int u, v, w; 73 Edge() {} 74 Edge(int uu, int vv, int ww) : u(uu), v(vv), w(ww) {} 75 }Edge; 76 77 const int maxn = 300030; 78 int n; 79 int ret; 80 int length[maxn]; 81 bool vis[maxn]; 82 vector<Edge> edge[maxn]; 83 84 int bfs(int start) { 85 Cls(vis); Cls(length); 86 queue<int> q; 87 q.push(start); 88 vis[start] = 1; 89 while(!q.empty()) { 90 int u = q.front(); q.pop(); 91 Rep(i, edge[u].size()) { 92 int v = edge[u][i].v; 93 int w = edge[u][i].w; 94 if(vis[v]) continue; 95 vis[v] = 1; 96 length[v] = length[u] + w; 97 q.push(v); 98 } 99 } 100 int aim = 0; 101 For(i, 1, n) { 102 if(length[aim] < length[i]) aim = i; 103 } 104 return aim; 105 } 106 107 int main() { 108 // FRead(); 109 int u, v, w; 110 while(~Rint(n)) { 111 ret = 0x7f7f7f; 112 Rep(i, n+1) edge[i].clear(); 113 Rep(i, n-1) { 114 Rint(u); Rint(v); 115 u--, v--, w = 1; 116 edge[u].push_back(Edge(u, v, w)); 117 edge[v].push_back(Edge(v, u, w)); 118 } 119 u = bfs(0); 120 v = bfs(u); 121 printf("%d ", length[v]); 122 } 123 RT 0; 124 }