Added Centroid Decomposition Library

c++/centroid_decomposition.cpp

@@ -0,0 +1,105 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+using namespace __gnu_pbds;
+template <typename T> using ordered_set = tree<T, null_type,less<T>, rb_tree_tag,tree_order_statistics_node_update>;
+// orderded_set ->  find_by_order(x)<itr, x being 0-indexed>; order_of_key(x)<count, strictly less>
+
+typedef long long       ll;
+typedef long double     lld;
+typedef pair<int, int>  pii;
+typedef pair<ll, ll>    pll;
+#define loop(n)         for(ll i = 0; i < (n); ++i)
+#define rep(i,zz,n)     for(ll i = zz; i < (n); ++i)
+#define repi(i,zz,n)    for(ll i = zz; i >= (n); --i)
+#define all(v)          v.begin(),v.end()
+#define pb              push_back
+#define ff              first
+#define ss              second
+#define sz(x)           (int)x.size()
+#define nline           cout << '\n'
+
+#define     debug(x)    cout << #x << " "; _print(x); cout << '\n';
+#define     _debug(a,b) cout << #a << " [ "; array_debug(a,b); cout << "]\n";
+template <class T, class V> void array_debug(T *a, V n){ rep(i,0,n) cout << a[i] << ' ';}
+template <class T>          void _print(T t) {cout << t;}
+template <class T, class V> void _print(pair <T, V> p) {cout << "{"; _print(p.ff); cout << ","; _print(p.ss); cout << "}";}
+template <class T>          void _print(vector <T> v) {cout << "[ "; for (T i : v) {_print(i); cout << " ";} cout << "]";}
+template <class T>          void _print(set <T> v) {cout << "[ "; for (T i : v) {_print(i); cout << " ";} cout << "]";}
+template <class T>          void _print(multiset <T> v) {cout << "[ "; for (T i : v) {_print(i); cout << " ";} cout << "]";}
+template <class T, class V> void _print(map <T, V> v) {cout << "[ "; for (auto i : v) {_print(i); cout << " ";} cout << "]";}
+
+const lld eps = 1e-9;
+const int mod = 1e9 + 7;
+const ll inf = 1e18;
+const int N1 = 2e5 + 10;
+
+// vector<vector<int>> adj;
+
+template<typename T>
+struct CentroidDecomposition {
+	vector<int> subtr, par_cd;
+	vector<bool> del;
+
+	void assign(int n) {
+		subtr = vector<int>(n);
+		par_cd = vector<int>(n);
+		del = vector<bool>(n);
+
+		decompose_cd(0, 0);
+	}
+
+	int get_subtree_size(int i, int j) {
+		subtr[i] = 1;
+		for (int x : adj[i]) {
+			if (x == j || del[x])  continue;
+			subtr[i] += get_subtree_size(x, i);
+		}
+		return subtr[i];
+	}
+
+	int find_centroid(int i, int j, int n) {
+		for (int x : adj[i]) {
+			if (x != j && !del[x] && subtr[x] * 2 > n) {
+				return find_centroid(x, i, n); 
+			}
+		}
+		return i;
+	}
+
+	void decompose_cd(int i, int j) {
+		int n = get_subtree_size(i, j);
+		int ct = find_centroid(i, j, n);
+		par_cd[ct] = j;     //  parent of centrid-node in centroid-tree
+
+		del[ct] = 1;
+		for (int x : adj[ct]) {
+			if (del[x])  continue;
+			decompose_cd(x, ct);
+		}
+	}
+};
+CentroidDecomposition<int> cd;
+
+int code() {
+
+	// enter main code
+
+	return 0;
+}
+
+int main() {
+	ios::sync_with_stdio(0); cin.tie(0);
+	// freopen("input.txt","r",stdin);
+	// freopen("output.txt","w",stdout);
+
+	int tc = 1;
+	cin >> tc;
+
+	loop(tc)  code();
+	// rep(i, 1, tc + 1)  cout << "Case #" << i << ": ", code();
+
+	return 0;
+}