Create count-unhappy-friends.cpp

Author: kamyu104

C++/count-unhappy-friends.cpp

@@ -0,0 +1,34 @@
+// Time:  O(n^2)
+// Space: O(n^2)
+
+class Solution {
+public:
+    int unhappyFriends(int n, vector<vector<int>>& preferences, vector<vector<int>>& pairs) {
+        vector<vector<int>> friends(n, vector<int>(n));
+        for (int i = 0; i < size(preferences); ++i) {
+            for (int j = 0; j < size(preferences[i]); ++j) {
+                friends[i][preferences[i][j]] = j;
+            }
+        }
+        vector<int> pairing(n);
+        for (const auto &p : pairs) {
+            pairing[p[0]] = p[1];
+            pairing[p[1]] = p[0];
+        }
+
+        int result = 0;
+        for (int i = 0; i < size(friends); ++i) {
+            for (int j = 0; j < size(friends[i]); ++j) {
+                if (j == i || j == pairing[i]) {
+                    continue;
+                }
+                if (friends[i][j] < friends[i][pairing[i]] &&
+                    friends[j][i] < friends[j][pairing[j]]) {
+                    ++result;
+                    break;
+                }
+            }
+        }
+        return result;
+    }
+};