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

Posted 2020-07-09

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。

  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 
 36 using namespace std;
 37 
 38 #define fr first
 39 #define sc second
 40 #define cl clear
 41 #define BUG puts("here!!!")
 42 #define W(a) while(a--)
 43 #define pb(a) push_back(a)
 44 #define Rint(a) scanf("%d", &a)
 45 #define Rll(a) scanf("%lld", &a)
 46 #define Rs(a) scanf("%s", a)
 47 #define Cin(a) cin >> a
 48 #define FRead() freopen("in", "r", stdin)
 49 #define FWrite() freopen("out", "w", stdout)
 50 #define Rep(i, len) for(int i = 0; i < (len); i++)
 51 #define For(i, a, len) for(int i = (a); i < (len); i++)
 52 #define Cls(a) memset((a), 0, sizeof(a))
 53 #define Clr(a, x) memset((a), (x), sizeof(a))
 54 #define Full(a) memset((a), 0x7f7f, sizeof(a))
 55 #define lrt rt << 1
 56 #define rrt rt << 1 | 1
 57 #define pi 3.14159265359
 58 #define RT return
 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 map<string, int> msi;
 65 typedef vector<LL> vl;
 66 typedef vector<vl> vvl;
 67 typedef vector<bool> vb;
 68 
 69 typedef struct Query {
 70     int idx;
 71     int u, v;
 72     Query() {}
 73     Query(int uu, int vv, int ii) : u(uu), v(vv), idx(ii) {}
 74 }Query;
 75 
 76 typedef struct Edge {
 77     int v, w;
 78     Edge() {}
 79     Edge(int vv, int ww) : v(vv), w(ww) {}
 80 }Edge;
 81 
 82 typedef struct Ans {
 83     int idx;
 84     int ans;
 85     Ans() {}
 86     Ans(int aa, int ii) :ans(aa), idx(ii) {}
 87 }Ans;
 88 
 89 const int maxn = 40010;
 90 const int maxm = 222;
 91 int n, m, qcnt, acnt;
 92 int depth[maxn];
 93 int in[maxn];
 94 bool vis[maxn];
 95 int pre[maxn];
 96 Query q[maxm];
 97 Ans ans[maxn];
 98 vector<Edge> G[maxn];
 99 int u, v, w;
100 
101 int find(int x) {
102     return x == pre[x] ? x : pre[x] = find(pre[x]);
103 }
104 
105 void unite(int x, int y) {
106     x = find(x);
107     y = find(y);
108     if(x != y) pre[y] = x;
109 }
110 
111 void dfs(int u, int d) {
112     // pre[u] = u;
113     depth[u] = d;
114     Rep(i, G[u].size()) {
115         int v = G[u][i].v;
116         if(!vis[v]) {
117             dfs(v, d+G[u][i].w);
118             unite(u, v);
119         }
120     }
121     vis[u] = 1;
122     Rep(i, qcnt) {
123         int uu = q[i].u;
124         int vv = q[i].v;
125         int idx = q[i].idx;
126         if(vis[uu] && vv == u) {
127             ans[acnt].idx = idx;
128             ans[acnt++].ans = abs(depth[vv] - depth[uu]);
129         }
130         if(vis[vv] && uu == u) {
131             ans[acnt].idx = idx;
132             ans[acnt++].ans = abs(depth[uu] - depth[vv]);
133         }
134     }
135 }
136 
137 bool cmp(Ans x, Ans y) {
138     return x.idx < y.idx;
139 }
140 
141 int main() {
142     // FRead();
143     int T;
144     Rint(T);
145     W(T) {
146         Rint(n); Rint(m);
147         Cls(vis); Cls(depth); Cls(ans); Cls(G);
148         acnt = qcnt = 0; Rep(i, n+5) G[i].cl(), pre[i] = i;
149         Rep(i, n-1) {
150             Rint(u); Rint(v); Rint(w);
151             G[u].push_back(Edge(v, w));
152             in[v]++;
153         }
154         Rep(i, m) {
155             Rint(u); Rint(v);
156             q[qcnt++] = Query(u, v, i);
157         }
158         For(i, 1, n+1) if(in[i] == 0) dfs(i, 0);
159         sort(ans, ans+acnt, cmp);
160         Rep(i, acnt) {
161             printf("%d\n", ans[i].ans);
162         }
163     }
164     RT 0;
165 }