Connections between cities（LCA）

 1 #include <cstdio>
 2 #include <vector>
 3 #include <cstring>
 4 using namespace std;
 5 
 6 const int maxn = 1e4 + 7;
 7 int n, m, q, u, v, k, cnt;
 8 int cost[maxn], deep[maxn], fa[maxn][30], vis[maxn];
 9 
10 struct edge {
11     int v, l;
12     edge(int v = 0, int l = 0) : v(v), l(l) {}
13 };
14 
15 vector<edge> G[maxn];
16 
17 void init() {
18     for(int i = 0; i <= n; i++) {
19         G[i].clear();
20     }
21     cnt = 0;
22     memset(vis, 0, sizeof(vis));
23     memset(cost, 0, sizeof(cost));
24 }
25 
26 void dfs(int u, int d, int p) {
27     fa[u][0] = p;
28     deep[u] = d;
29     vis[u] = cnt;
30     for(int i = 0; i < G[u].size(); i++) {
31         int v = G[u][i].v;
32         if(v != p) {
33             cost[v] = cost[u] + G[u][i].l;
34             dfs(v, d + 1, u);
35         }
36     }
37 }
38 
39 void lca() {
40     for(int i = 1; i <= n; i++) {
41         for(int j = 1; (1 << j) <= n; j++) {
42             fa[i][j] = -1;
43         }
44     }
45     for(int j = 1; (1 << j) <= n; j++) {
46         for(int i = 1; i <= n; i++) {
47             if(fa[i][j-1] != -1) {
48                 fa[i][j] = fa[fa[i][j-1]][j-1];
49             }
50         }
51     }
52 }
53 
54 int query(int u, int v) {
55     if(deep[u] < deep[v]) swap(u, v);
56     int k;
57     for(k = 0; (1 << (k+1)) <= deep[u]; k++);
58     for(int i = k; i >= 0; i--) {
59         if(deep[u] - (1 << i) >= deep[v]) {
60             u = fa[u][i];
61         }
62     }
63     if(u == v) return u;
64     for(int i = k; i >= 0; i--) {
65         if(fa[u][i] != -1 && fa[u][i] != fa[v][i]) {
66             u = fa[u][i];
67             v = fa[v][i];
68         }
69     }
70     return fa[u][0];
71 }
72 
73 int main() {
74     while(~scanf("%d%d%d", &n, &m, &q)) {
75         init();
76         while(m--) {
77             scanf("%d%d%d", &u, &v, &k);
78             G[u].push_back(edge(v, k));
79             G[v].push_back(edge(u, k));
80         }
81         for(int i = 1; i <= n; i++) {
82             if(vis[i] == 0) {
83                 cnt++;
84                 dfs(i, 0, -1);
85             }
86         }
87         lca();
88         for(int i = 0; i < q; i++) {
89             scanf("%d%d", &u, &v);
90             if(vis[u] != vis[v]) {
91                 printf("Not connected\n");
92             } else {
93                 printf("%d\n", cost[u] + cost[v] - 2 * cost[query(u,v)]);
94             }
95         }
96     }
97     return 0;
98 }