Create redundant-connection.cpp

kamyu104 · web-flow · commit de8b9bc8d9d9 · 2017-09-24T16:50:39.000+08:00
diff --git a/C++/redundant-connection.cpp b/C++/redundant-connection.cpp
@@ -0,0 +1,48 @@
+// Time:  O(nlog*n) ~= O(n), n is the length of the positions
+// Space: O(n)
+
+class Solution {
+public:
+    vector<int> findRedundantConnection(vector<vector<int>>& edges) {
+        UnionFind union_find(2000);
+        for (const auto& edge : edges) {
+            if (!union_find.union_set(edge[0], edge[1])) {
+                return edge;
+            }
+        }
+        return {};
+    }
+
+private:
+    class UnionFind {
+        public:
+            UnionFind(const int n) : set_(n), count_(n) {
+                iota(set_.begin(), set_.end(), 0);
+            }
+
+            int find_set(const int x) {
+               if (set_[x] != x) {
+                   set_[x] = find_set(set_[x]);  // Path compression.
+               }
+               return set_[x];
+            }
+
+            bool union_set(const int x, const int y) {
+                int x_root = find_set(x), y_root = find_set(y);
+                if (x_root == y_root) {
+                    return false;
+                }
+                set_[min(x_root, y_root)] = max(x_root, y_root);
+                --count_;
+                return true;
+            }
+
+            int length() const {
+                return count_;
+            }
+
+        private:
+            vector<int> set_;
+            int count_;
+    };
+};
