Create get-watched-videos-by-your-friends.cpp

Author: kamyu104

C++/get-watched-videos-by-your-friends.cpp

@@ -0,0 +1,40 @@
+// Time:  O(n + vlogv), v is the number of the level videos
+// Space: O(w)
+
+class Solution {
+public:
+    vector<string> watchedVideosByFriends(vector<vector<string>>& watchedVideos, vector<vector<int>>& friends, int id, int level) {
+        vector<int> curr_level = {id};
+        unordered_set<int> lookup = {id};
+        for (int i = 0; i < level; ++i) {
+            vector<int> new_level;
+            for (const auto& i : curr_level) {
+                for (const auto& j : friends[i]) {
+                    if (lookup.count(j)) {
+                        continue;
+                    }
+                    lookup.emplace(j);
+                    new_level.emplace_back(j);
+                }
+            }
+            curr_level = move(new_level);
+        }
+
+        unordered_map<string, int> count;
+        for (const auto& i : curr_level) {
+            for (const auto& v : watchedVideos[i]) {
+                ++count[v];
+            }
+        }
+        vector<string> result;
+        transform(count.cbegin(), count.cend(), back_inserter(result),
+                  [](const auto& x) {
+                      return x.first;
+                  });
+        sort(result.begin(), result.end(),
+             [&count](const auto& a, const auto& b) {
+                 return make_pair(count[a], a) < make_pair(count[b], b);
+             });
+        return result;
+    }
+};