Create accounts-merge.cpp

Author: kamyu104

C++/accounts-merge.cpp

@@ -0,0 +1,63 @@
+// Time:  O(nlogn), n is the number of total emails, and the max length of email is 320, p.s. {64}@{255}
+// Space: O(n)
+
+class Solution {
+public:
+    vector<vector<string>> accountsMerge(vector<vector<string>>& accounts) {
+        UnionFind union_find;
+        unordered_map<string, string> email_to_name;
+        unordered_map<string, int> email_to_id;
+        for (const auto& account : accounts) {
+            const auto& name = account[0];
+            for (int i = 1; i < account.size(); ++i) {
+                if (!email_to_id.count(account[i])) {
+                    email_to_name[account[i]] = name;
+                    email_to_id[account[i]] = union_find.get_id();
+                }
+                union_find.union_set(email_to_id[account[1]], email_to_id[account[i]]);
+            }
+        }
+
+        unordered_map<int, set<string>> lookup; 
+        for (const auto& kvp : email_to_name) {
+            const auto& email = kvp.first;
+            lookup[union_find.find_set(email_to_id[email])].emplace(email);
+        }
+        vector<vector<string>> result;
+        for (const auto& kvp : lookup) {
+            const auto& emails = kvp.second;
+            vector<string> tmp{email_to_name[*emails.begin()]};
+            for (const auto& email : emails) {
+                tmp.emplace_back(email);
+            }
+            result.emplace_back(move(tmp));
+        }
+        return result;
+    }
+
+private:
+    class UnionFind {
+        public:
+            int get_id() {
+                set_.emplace_back(set_.size());
+                return set_.size() - 1;
+            }
+
+            int find_set(const int x) {
+               if (set_[x] != x) {
+                   set_[x] = find_set(set_[x]);  // Path compression.
+               }
+               return set_[x];
+            }
+
+            void union_set(const int x, const int y) {
+                int x_root = find_set(x), y_root = find_set(y);
+                if (x_root != y_root) {
+                    set_[min(x_root, y_root)] = max(x_root, y_root);
+                }
+            }
+
+        private:
+            vector<int> set_;
+    };
+};