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LCA.cpp
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LCA.cpp
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struct LCA_orz {
int id = 0;
int h[N], tin[M], tout[M], euler[M], LOG[M];
struct node {
int h, v;
bool operator < (const node &o) const {
return h < o.h;
}
} mn[18][M];
void dfs(int v) {
euler[++id] = v;
for (auto u : adj[v]) {
if (h[u] == 0) {
h[u] = h[v] + 1;
dfs(u);
euler[++id] = v;
}
}
}
void setup() {
for (int i = 1; i < M; ++i) {
LOG[i] = (i & 1) ? LOG[i - 1] : LOG[i >> 1] + 1;
}
for (int j = 0; j <= 17; ++j) {
for (int i = 1; i <= id; ++i) {
mn[j][i].h = INT_MAX;
}
}
dfs(h[1] = 1);
memset(tin, 0x3f, sizeof tin);
for (int i = 1; i <= id; ++i) {
int x = euler[i];
tin[x] = min(tin[x], i);
tout[x] = max(tout[x], i);
mn[0][i] = {h[x], x};
}
for (int j = 1; j <= 17; ++j) {
for (int i = 1; i <= id - (1 << j) + 1; ++i) {
mn[j][i] = min(mn[j - 1][i], mn[j - 1][i + (1 << (j - 1))]);
}
}
}
int get_min(int l, int r) {
int k = LOG[r - l + 1];
return min(mn[k][l], mn[k][r - (1 << k) + 1]).v;
}
int get(int u, int v) {
return get_min(min(tin[u], tin[v]), max(tout[u], tout[v]));
}
} LCA;