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LowestCommonAncestor.hpp
55 lines (53 loc) · 1.78 KB
/
LowestCommonAncestor.hpp
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// edgeを貼ったあとにbuild()を忘れない!
struct TreeDoubling {
struct Edge {
int to, len;
}; // 場合に応じて書き換える、toは必須
std::vector<std::vector<Edge>> g;
int n, size; // MSB + 1
int root;
std::vector<int> depth;
std::vector<std::vector<int>> parent; // ダミー頂点n(親もn)
TreeDoubling(int n_) : g(n_), n(n_), size(64 - __builtin_clzll(n_) + 1), depth(n_) {
parent.resize(size, std::vector<int>(n + 1, n));
}
void build(int root_ = 0) {
auto dfs = [&](auto f, int v, int prv) -> void {
for (Edge& e : g[v]) {
if (e.to == prv) continue;
depth[e.to] = depth[v] + e.len;
parent[0][e.to] = v;
f(f, e.to, v);
}
};
root = root_;
depth[root] = 0;
dfs(dfs, root, -1);
for (int k = 0; k < size - 1; k++) {
for (int i = 0; i < n; i++) {
parent[k + 1][i] = parent[k][parent[k][i]];
}
}
}
// vからd個分親にさかのぼった頂点、rootよりも上はnを返す
int query(int v, int d) {
int ret = v;
for (int j = 0; j < size; j++) {
if (d >> j & 1) ret = parent[j][ret];
}
return ret;
}
int lca(int u, int v) {
if (depth[u] > depth[v]) std::swap(u, v);
v = query(v, depth[v] - depth[u]);
if (u == v) return u;
for (int j = size - 1; j >= 0; j--) {
if (parent[j][u] == parent[j][v]) continue;
u = parent[j][u];
v = parent[j][v];
}
assert(parent[0][u] == parent[0][v]);
return parent[0][u];
}
int dist(int u, int v) { return depth[u] + depth[v] - depth[lca(u, v)] * 2; }
};