From 5ab8a5088b729a9953b8dff1b2a985dc8fb2098b Mon Sep 17 00:00:00 2001
From: mzuenni <michi.zuendorf@gmail.com>
Date: Mon, 27 Jun 2022 17:19:28 +0200
Subject: updated tcr

---
 datastructures/waveletTree.cpp | 48 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 datastructures/waveletTree.cpp

(limited to 'datastructures/waveletTree.cpp')

diff --git a/datastructures/waveletTree.cpp b/datastructures/waveletTree.cpp
new file mode 100644
index 0000000..feef2d4
--- /dev/null
+++ b/datastructures/waveletTree.cpp
@@ -0,0 +1,48 @@
+struct WaveletTree {
+	using it = vector<ll>::iterator;
+	WaveletTree *ln, *rn;
+	ll lo, hi;
+	vector<int> b;
+
+private:
+	WaveletTree(it from, it to, ll x, ll y)
+	: ln(nullptr), rn(nullptr), lo(x), hi(y), b(1) {
+		ll mid = (lo + hi) / 2;
+		auto f = [&](ll x){return x < mid;};
+		for (it c = from; c != to; c++) {
+			b.push_back(b.back() + f(*c));
+		}
+		if (lo + 1 >= hi || from == to) return;
+		it pivot = stable_partition(from, to, f);
+		ln = new WaveletTree(from, pivot, lo, mid);
+		rn = new WaveletTree(pivot, to, mid, hi);
+	}
+
+public:
+	WaveletTree(vector<ll> in) : WaveletTree(all(in), 
+		*min_element(all(in)), *max_element(all(in)) + 1){}
+
+	// kth element in sort[l, r) all 0-indexed
+	ll kth(int l, int r, int k) {
+		if (l >= r || k >= r - l) return -1;
+		if (lo + 1 >= hi) return lo;
+		int inLeft = b[r] - b[l];
+		if (k < inLeft) {
+			return ln->kth(b[l], b[r], k);
+		} else {
+			return rn->kth(l-b[l], r-b[r], k-inLeft);
+	}}
+
+	// count elements in[l, r) smaller than k
+	int countSmaller(int l, int r, ll k) {
+		if (l >= r || k <= lo) return 0;
+		if (hi <= k) return r - l;
+		return ln->countSmaller(b[l], b[r], k) + 
+					 rn->countSmaller(l-b[l], r-b[r], k);
+	}
+
+	~WaveletTree(){
+		delete ln;
+		delete rn;
+	}
+};
-- 
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