updated tcr

1 files changed, 27 insertions, 0 deletions

diff --git a/math/inversionsMerge.cpp b/math/inversionsMerge.cpp
new file mode 100644
index 0000000..1ea2ada
--- /dev/null
+++ b/math/inversionsMerge.cpp
@@ -0,0 +1,27 @@
+// Laufzeit: O(n*log(n))
+ll merge(vector<ll>& v, vector<ll>& left, vector<ll>& right) {
+	int a = 0, b = 0, i = 0;
+	ll inv = 0;
+	while (a < (int)left.size() && b < (int)right.size()) {
+		if (left[a] < right[b]) v[i++] = left[a++];
+		else {
+			inv += left.size() - a;
+			v[i++] = right[b++];
+		}
+	}
+	while (a < (int)left.size()) v[i++] = left[a++];
+	while (b < (int)right.size()) v[i++] = right[b++];
+	return inv;
+}
+
+ll mergeSort(vector<ll> &v) { // Sortiert v und gibt Inversionszahl zurück.
+	int n = v.size();
+	vector<ll> left(n / 2), right((n + 1) / 2);
+	for (int i = 0; i < n / 2; i++) left[i] = v[i];
+	for (int i = n / 2; i < n; i++) right[i - n / 2] = v[i];
+
+	ll result = 0;
+	if (left.size() > 1) result += mergeSort(left);
+	if (right.size() > 1) result += mergeSort(right);
+	return result + merge(v, left, right);
+}