Create 1636.cpp

LeetCode/1636.cpp

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+
+class Solution {
+public:
+    vector<int> frequencySort(vector<int>& nums) {
+        unordered_map<int, int> freq;
+        map<int, set<int>> keys;
+
+        int n = nums.size();
+
+        for (int i = 0; i < n; i++) {
+            auto iter = freq.find(nums[i]);
+            if (iter != freq.end()) {
+                keys[iter->second].erase(nums[i]);
+                iter->second++;
+                keys[iter->second].insert(nums[i]);
+            }
+            else {
+                freq.insert_or_assign(nums[i], 1);
+                keys[1].insert(nums[i]);
+            }
+        }
+
+        vector<int> result;
+        for (auto iter = keys.begin(); iter != keys.end(); iter++) {
+            for (auto xiter = iter->second.rbegin(); xiter != iter->second.rend(); xiter++) {
+                for (int i = 0; i < iter->first; i++) {
+                    result.push_back(*xiter);
+                }
+            }
+        }
+
+        return result;
+    }
+};