Update number-of-connected-components-in-an-undirected-graph.cpp

Author: kamyu104

C++/number-of-connected-components-in-an-undirected-graph.cpp

@@ -18,7 +18,7 @@ class Solution {
                 iota(set_.begin(), set_.end(), 0);
             }
 
-            int find_set(int x) {
+            int find_set(const int x) {
                if (set_[x] != x) {
                    set_[x] = find_set(set_[x]);  // Path compression.
                }