diff --git a/trees/quick_union.cc b/trees/quick_union.cc
index 32b6e32..465654e 100644
--- a/trees/quick_union.cc
+++ b/trees/quick_union.cc
@@ -1,9 +1,10 @@
 class quick_union {
 private:
-    vector<size_t> c;
+    vector<size_t> c, sz;
 public:
-    quick_union(size_t n) : c(n) {
+    quick_union(size_t n) : c(n), sz(n) {
         iota(c.begin(), c.end(), 0);
+        sz.assign(n, 1);
     }
     
     size_t query(size_t i) {
@@ -12,11 +13,15 @@ public:
     }
     
     void merge(size_t i, size_t j) {
+        sz[query(j)] += sz[query(i)];
         c[query(i)] = query(j);
     }
 
     bool connected(size_t i, size_t j) {
         return query(i) == query(j);
     }
-};
 
+    size_t query_size(size_t i) {
+        return sz[query(i)];
+    }
+};