unordered_map and set and iterator manipulation

Author: Adam Lin

1207_uniqueOccurrences.cpp

@@ -0,0 +1,36 @@
+class Solution {
+public:
+    bool uniqueOccurrences(vector<int>& arr) {
+        unordered_map<int, int> umap; // Map to store frequency of each element in arr
+        set<int> frequency; // Set to store unique frequencies
+
+        // Count the frequency of each element in arr
+        for(int i = 0; i < arr.size(); ++i){
+            umap[arr[i]]++;
+        }
+        // Example: arr = [1,2,2,1,1,3] -> umap = {{1, 3}, {2, 2}, {3, 1}}
+
+        // Check if all frequencies are unique
+        for(auto it : umap){
+            // Check if the frequency already exists in the set
+            if(frequency.find(it.second) != frequency.end()){
+                // If the frequency already exists, it means the occurrences are not unique
+                // frequency.find(value) searches the set for the given value.
+                //If the value is found, it returns an iterator pointing to that element.
+                //If the value is not found, it returns frequency.end(), which is a special iterator indicating the end of the set.
+                return false; // Return false since we found a duplicate frequency
+            } 
+            frequency.insert(it.second); // Insert frequency into set
+        }
+
+        return true; // All frequencies are unique
+    }
+};
+/*
+The variable it is actually an instance of std::pair<const int, int> because umap is an unordered_map<int, int>. Each element in an unordered map is stored as a key-value pair, where the key is of type int and the value is also of type int. Therefore, it represents a pair consisting of key and value.
+
+For std::pair, you can access:
+
+it.first which gives you the key.
+it.second which gives you the value (in this case, the frequency of the element).
+*/