[HDOJ2586]How far away?（最近公共祖先, 离线tarjan, 并查集）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2586

这题以前做过…现在用tarjan搞一发…竟然比以前暴力过的慢…………

由于是离线算法，需要Query来保存查询数据，Ans来保存结果。最后输出的时候按照idx的顺序输出，所以胡搞了个排序。。

dfs每次更新depth，当前点depth是上一个点累积下来的。

 /*
 ━━━━━┒ギリギリ♂ eye！
 ┓┏┓┏┓┃キリキリ♂ mind！
 ┛┗┛┗┛┃＼○／
 ┓┏┓┏┓┃ /
 ┛┗┛┗┛┃ノ)
 ┓┏┓┏┓┃
 ┛┗┛┗┛┃
 ┓┏┓┏┓┃
 ┛┗┛┗┛┃
 ┓┏┓┏┓┃
 ┛┗┛┗┛┃
 ┓┏┓┏┓┃
 ┃┃┃┃┃┃
 ┻┻┻┻┻┻
 */
 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 #include <cstring>
 #include <climits>
 #include <complex>
 #include <fstream>
 #include <cassert>
 #include <cstdio>
 #include <bitset>
 #include <vector>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <ctime>
 #include <set>
 #include <map>
 #include <cmath>

 using namespace std;

 #define fr first
 #define sc second
 #define cl clear
 #define BUG puts("here!!!")
 #define W(a) while(a--)
 #define pb(a) push_back(a)
 #define Rint(a) scanf("%d", &a)
 #define Rll(a) scanf("%lld", &a)
 #define Rs(a) scanf("%s", a)
 #define Cin(a) cin >> a
 #define FRead() freopen("in", "r", stdin)
 #define FWrite() freopen("out", "w", stdout)
 #define Rep(i, len) for(int i = 0; i < (len); i++)
 #define For(i, a, len) for(int i = (a); i < (len); i++)
 #define Cls(a) memset((a), 0, sizeof(a))
 #define Clr(a, x) memset((a), (x), sizeof(a))
 #define Full(a) memset((a), 0x7f7f, sizeof(a))
 #define lrt rt << 1
 #define rrt rt << 1 | 1
 #define pi 3.14159265359
 #define RT return
 typedef long long LL;
 typedef long double LD;
 typedef unsigned long long ULL;
 typedef pair<int, int> pii;
 typedef pair<string, int> psi;
 typedef map<string, int> msi;
 typedef vector<LL> vl;
 typedef vector<vl> vvl;
 typedef vector<bool> vb;

 typedef struct Query {
     int idx;
     int u, v;
     Query() {}
     Query(int uu, int vv, int ii) : u(uu), v(vv), idx(ii) {}
 }Query;

 typedef struct Edge {
     int v, w;
     Edge() {}
     Edge(int vv, int ww) : v(vv), w(ww) {}
 }Edge;

 typedef struct Ans {
     int idx;
     int ans;
     Ans() {}
     Ans(int aa, int ii) :ans(aa), idx(ii) {}
 }Ans;

 const int maxn = ;
 const int maxm = ;
 int n, m, qcnt, acnt;
 int depth[maxn];
 int in[maxn];
 bool vis[maxn];
 int pre[maxn];
 Query q[maxm];
 Ans ans[maxn];
 vector<Edge> G[maxn];
 int u, v, w;

 int find(int x) {
     return x == pre[x] ? x : pre[x] = find(pre[x]);
 }

 void unite(int x, int y) {
     x = find(x);
     y = find(y);
     if(x != y) pre[y] = x;
 }

 void dfs(int u, int d) {
     // pre[u] = u;
     depth[u] = d;
     Rep(i, G[u].size()) {
         int v = G[u][i].v;
         if(!vis[v]) {
             dfs(v, d+G[u][i].w);
             unite(u, v);
         }
     }
     vis[u] = ;
     Rep(i, qcnt) {
         int uu = q[i].u;
         int vv = q[i].v;
         int idx = q[i].idx;
         if(vis[uu] && vv == u) {
             ans[acnt].idx = idx;
             ans[acnt++].ans = abs(depth[vv] - depth[uu]);
         }
         if(vis[vv] && uu == u) {
             ans[acnt].idx = idx;
             ans[acnt++].ans = abs(depth[uu] - depth[vv]);
         }
     }
 }

 bool cmp(Ans x, Ans y) {
     return x.idx < y.idx;
 }

 int main() {
     // FRead();
     int T;
     Rint(T);
     W(T) {
         Rint(n); Rint(m);
         Cls(vis); Cls(depth); Cls(ans); Cls(G);
         acnt = qcnt = ; Rep(i, n+) G[i].cl(), pre[i] = i;
         Rep(i, n-) {
             Rint(u); Rint(v); Rint(w);
             G[u].push_back(Edge(v, w));
             in[v]++;
         }
         Rep(i, m) {
             Rint(u); Rint(v);
             q[qcnt++] = Query(u, v, i);
         }
         For(i, , n+) if(in[i] == ) dfs(i, );
         sort(ans, ans+acnt, cmp);
         Rep(i, acnt) {
             printf("%d\n", ans[i].ans);
         }
     }
     RT ;
 }