Index: lib/typical/coordinate_compression.cpp
==================================================================
--- lib/typical/coordinate_compression.cpp
+++ lib/typical/coordinate_compression.cpp
@@ -1,17 +1,20 @@
-// Convert a list of distinct elements to [0..N), preserving the original order.
-// O(N log N), but doesn't incur the overhead of std::map.
-// Tested: TCO 2012 R2C Mid
+// Convert a list of N elements with K distinct elements to [origin .. origin+K),
+// preserving the original order.  O(N log N), but doesn't incur the overhead of std::map.
+// Tested: TCO 2012 R2C Mid, SRM 584 Mid
 
 template<typename T>
-std::vector<int> compress(std::vector<T>& xs)
+vector<int> compress(const vector<T>& xs, int origin = 0)
 {
-	std::vector< pair<T,int> > xi;
+	vector< pair<T,int> > xi;
 	for(int i=0; i<xs.size(); ++i)
 		xi.push_back( make_pair(xs[i], i) );
 	sort(xi.begin(), xi.end());
 
-	std::vector<int> result(xs.size());
-	for(int k=0; k<xi.size(); ++k)
-		result[xi[k].second] = k;
+	vector<int> result(xs.size());
+	for(int k=0,id=origin; k<xi.size(); ++k) {
+		if(0<=k-1 && xi[k-1].first<xi[k].first)
+			++id;
+		result[xi[k].second] = id;
+	}
 	return result;
 }