1 files changed, 32 insertions, 0 deletions
diff --git a/content/datastructures/waveletTree.cpp b/content/datastructures/waveletTree.cpp
new file mode 100644
index 0000000..55167b6
--- /dev/null
+++ b/content/datastructures/waveletTree.cpp
@@ -0,0 +1,32 @@
+struct WaveletTree {
+	unique_ptr<WaveletTree> ln, rn;
+	vector<int> b = {0};
+	ll lo, hi;
+
+	WaveletTree(auto in) : lo(*ranges::min_element(in)),
+	                       hi(*ranges::max_element(in) + 1) {
+		ll mid = (lo + hi) / 2;
+		auto f = [&](ll x) { return x < mid; };
+		for (ll x: in) b.push_back(b.back() + f(x));
+		if (lo + 1 >= hi) return;
+		auto right = ranges::stable_partition(in, f);
+		ln = make_unique<WaveletTree>(
+		  ranges::subrange(begin(in), begin(right)));
+		rn = make_unique<WaveletTree>(right);
+	}
+
+	ll kth(int l, int r, int k) {
+		if (k < 0 || l + k >= r) 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);
+	}
+
+	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);
+	}
+};