1 files changed, 14 insertions, 0 deletions
diff --git a/math/permIndex.cpp b/math/permIndex.cpp
new file mode 100644
index 0000000..09ff7f7
--- /dev/null
+++ b/math/permIndex.cpp
@@ -0,0 +1,14 @@
+ll permIndex(vector<ll> v) {
+	Tree<ll> t;
+	reverse(all(v));
+	for (ll& x : v) {
+		t.insert(x);
+		x = t.order_of_key(x);
+	}
+	ll res = 0;
+	for (ll i = sz(v); i > 0; i--) {
+		res *= i;
+		res += v[i - 1];
+	}
+	return res;
+}