POJ 1986 LCA

链接：

http://poj.org/problem?id=1986

代码：

 31 struct edge { int to, weight; };
 32 vector<edge> G[MAXN];
 33 int vs[MAXN * 2 - 1];
 34 int depth[MAXN * 2 - 1];
 35 int id[MAXN];
 36 int dist[MAXN];
 37 
 38 int bit[MAXN * 2 - 1][16];
 39 
 40 void rmq_init(int n) {
 41     rep(i, 0, n) bit[i][0] = i;
 42     for (int j = 1; (1 << j) < n; j++)
 43         for (int i = 0; i + (1 << j) - 1 < n; i++){
 44             if (depth[bit[i][j - 1]] <= depth[bit[i + (1 << (j - 1))][j - 1]])
 45                 bit[i][j] = bit[i][j - 1];
 46             else bit[i][j] = bit[i + (1 << (j - 1))][j - 1];
 47         }
 48 }
 49 
 50 int query(int l, int r)
 51 {
 52     int k = 0;
 53     while ((1 << (k + 1)) < r - l + 1) k++;
 54     if (depth[bit[l][k]] <= depth[bit[r - (1 << k)][k]])
 55         return bit[l][k];
 56     else return bit[r - (1 << k)][k];
 57 }
 58 
 59 void dfs(int v, int p, int d, int &k) {
 60     id[v] = k;
 61     vs[k] = v;
 62     depth[k++] = d;
 63     rep(i, 0, G[v].size()) if (G[v][i].to != p) {
 64         dist[G[v][i].to] = dist[v] + G[v][i].weight;
 65         dfs(G[v][i].to, v, d + 1, k);
 66         vs[k] = v;
 67         depth[k++] = d;
 68     }
 69 }
 70 
 71 void init(int V) {
 72     int k = 0, root = 0;
 73     dfs(root, -1, 0, k);
 74     rmq_init(V * 2 - 1);
 75 }
 76 
 77 int lca(int u, int v) {
 78     return vs[query(min(id[u], id[v]), max(id[u], id[v]) + 1)];
 79 }
 80 
 81 int main() {
 82     int n, m;
 83     cin >> n >> m;
 84     int u, v, w;
 85     char c;
 86     while (m--) {
 87         scanf("%d%d%d %c", &u, &v, &w, &c);
 88         u--, v--;
 89         G[u].pb(edge{ v,w });
 90         G[v].pb(edge{ u,w });
 91     }
 92     init(n);
 93     int k;
 94     cin >> k;
 95     while (k--) {
 96         int u, v;
 97         scanf("%d%d", &u, &v);
 98         u--, v--;
 99         int t = lca(u, v);
100         int ans = dist[u] - dist[t] + dist[v] - dist[t];
101         printf("%d\n", ans);
102     }
103     return 0;
104 }