Create before-and-after-puzzle.cpp

Author: kamyu104

C++/before-and-after-puzzle.cpp

@@ -0,0 +1,34 @@
+// Time:  O(l * rlogr)  , l is the max length of phrases
+//                      , r is the number of result, could be up to O(n^2)
+// Space: O(l * (n + r)), n is the number of phrases
+
+class Solution {
+public:
+    vector<string> beforeAndAfterPuzzles(vector<string>& phrases) {
+        unordered_map<string, vector<size_t>> lookup;
+        for (int i = 0; i < phrases.size(); ++i) {
+            const auto& phrase = phrases[i];
+            const auto& right = phrase.rfind(' ');
+            const auto& word = (right == string::npos) ? phrase : phrase.substr(right + 1);
+            lookup[word].emplace_back(i);
+        }
+        unordered_set<string> result_set;
+        for (int i = 0; i < phrases.size(); ++i) {
+            const auto& phrase = phrases[i];
+            const auto& left = phrase.find(' ');
+            const auto& word = (left == string::npos) ? phrase : phrase.substr(0, left);
+            if (!lookup.count(word)) {
+                continue;
+            }
+            for (const auto& j : lookup[word]) {
+                if (j == i) {
+                    continue;
+                }
+                result_set.emplace(phrases[j] + phrase.substr(word.length()));
+            }
+        }
+        vector<string> result(result_set.cbegin(), result_set.cend());
+        sort(result.begin(), result.end());
+        return result;
+    }
+};