POJ 1986：Distance Queries（倍增求LCA）

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <queue>
 5 using namespace std;
 6 #define N 100010
 7 struct Edge {
 8     int v, nxt, w;
 9     Edge () {}
10     Edge (int v, int nxt, int w) : v(v), nxt(nxt), w(w) {}
11 } edge[N];
12 int dp[N][30], dep[N], dis[N], fa[N], head[N], tot, n;
13 
14 void Add(int u, int v, int w) {
15     edge[tot] = Edge(v, head[u], w); head[u] = tot++;
16     edge[tot] = Edge(u, head[v], w); head[v] = tot++;
17 }
18 
19 void DFS(int u) {
20     dp[u][0] = fa[u];
21     for(int i = 1; i <= 20; i++) // 转移
22         dp[u][i] = dp[dp[u][i-1]][i-1];
23     for(int i = head[u]; ~i; i = edge[i].nxt) {
24         int v = edge[i].v;
25         if(v == fa[u]) continue;
26         fa[v] = u;
27         dep[v] = dep[u] + 1;
28         dis[v] = dis[u] + edge[i].w;
29         DFS(v);
30     }
31 }
32 
33 int LCA(int x, int y) {
34     if(dep[x] < dep[y]) swap(x, y); //设x为较深的点
35     for(int i = 20; i >= 0; i--) // 让x跑到和y同一深度
36         if(dep[dp[x][i]] >= dep[y]) x = dp[x][i];
37     if(x == y) return x;
38     for(int i = 20; i >= 0; i--) // x和y同时向上跑
39         if(dp[x][i] != dp[y][i])
40             x = dp[x][i], y = dp[y][i];
41     return dp[x][0];
42 }
43 
44 int main() {
45     int m, q;
46     while(~scanf("%d%d", &n, &m)) {
47         memset(dp, 0, sizeof(dp));
48         memset(dis, 0, sizeof(dis));
49         memset(dep, 0, sizeof(dep));
50         memset(head, -1, sizeof(head));
51         tot = 0; char s[4];
52         for(int i = 0; i < m; i++) {
53             int u, v, w;
54             scanf("%d%d%d%s", &u, &v, &w, s);
55             Add(u, v, w);
56         }
57         fa[1] = 1; dis[1] = dep[1] = 0;
58         DFS(1);
59         scanf("%d", &q);
60         while(q--) {
61             int u, v;
62             scanf("%d%d", &u, &v);
63             printf("%d\n", dis[u] + dis[v] - dis[LCA(u, v)] * 2);
64         }
65     }
66     return 0;
67 }