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centroid decomposition.cpp
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centroid decomposition.cpp
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/**
* Usage centroid_decomposition c1(size,root);
*/
//LCA stuff here
class centroid_decomposition {
private:
int n, tot;
vector <int> par, lvl, tsz, dead;
void gettsz(int u, int p) {
tot++;
tsz[u] = 1;
for (auto v : adjlst[u]) {
if (v != p && !dead[v]) {
gettsz(v, u);
tsz[u] += tsz[v];
}
}
}
int find_centroid(int u, int p) {
for (auto v : adjlst[u]) {
if (v != pr && !dead[v]) {
if (tsz[v] > (tot / 2))
return find_centroid(v, u);
}
}
return u;
}
void decompose(int u, int p, int l) {
tot = 0;
gettsz(u, u);
int centro = find_centroid(u, u);
par[centro] = (p? p: centro);
lvl[centro] = l;
dead[centro] = 1;
for (auto v : adjlst[centro])
if (!dead[v])
decompose(v, centro, l + 1);
}
public:
centroid_decomposition(int size, int root) {
n = size;
par.assign(n + 1, 0);
lvl.reserve(n + 1);
tsz.reserve(n + 1);
dead.assign(n + 1, 0);
pre_lca(root);
decompose(root, 0, 1);
}
int lca(int u, int v) {
if (lvl[u] > lvl[v])
swap(u, v);
while (lvl[u] != lvl[v])
v = par[v];
while (u != v) {
u = par[u];
v = par[v];
}
return u;
}
void update(int u) {
int v = u;
while (true) {
//update logic
if (v == par[v])
break;
v = par[v];
}
}
int query(int u) {
int v = u;
int ans = 0;//Assign suitable value
while (1) {
//query logic
if (v == par[v])
break;
v = par[v];
}
return ans;
}
};