Add some heap solutions

Author: kiranpalsingh1806

README.md

@@ -253,10 +253,10 @@
 
 |S.No|Problem|Difficulty|Solution|
 |-|------|--------|------|
-|1|[Sort Array By Increasing Frequency](https://leetcode.com/problems/sort-array-by-increasing-frequency/)|Easy|[Solution](/solutions/heaps)|
-|2|[Kth Largest Element in An Array](https://leetcode.com/problems/kth-largest-element-in-an-array/)|Medium|[Solution](/solutions/heaps)|
-|3|[Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/)|Medium|[Solution](/solutions/heaps)|
-|4|[Sort Characters By Frequency](https://leetcode.com/problems/sort-characters-by-frequency/)|Medium|[Solution](/solutions/heaps)|
+|1|[Sort Array By Increasing Frequency](https://leetcode.com/problems/sort-array-by-increasing-frequency/)|Easy|[Solution](/solutions/heaps/sort-array-by-increasing-frequency.md)|
+|2|[Kth Largest Element in An Array](https://leetcode.com/problems/kth-largest-element-in-an-array/)|Medium|[Solution](/solutions/heaps/kth-largest-element-in-array.md)|
+|3|[Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/)|Medium|[Solution](/solutions/heaps/top-k-frequent-elements.md)|
+|4|[Sort Characters By Frequency](https://leetcode.com/problems/sort-characters-by-frequency/)|Medium|[Solution](/solutions/heaps/sort-characters-by-frequency.md)|
 |5|[Find K Closest Elements](https://leetcode.com/problems/find-k-closest-elements/)|Medium|[Solution](/solutions/heaps)|
 |6|[Top K Frequent Words](https://leetcode.com/problems/top-k-frequent-words/)|Medium|[Solution](/solutions/heaps)|
 |7|[K Closest Points To Origin](https://leetcode.com/problems/k-closest-points-to-origin/)|Medium|[Solution](/solutions/heaps)|

solutions/heaps/kth-largest-element-in-array.md

@@ -0,0 +1,17 @@
+## Kth Largest Element in Array
+
+```cpp
+class Solution {
+public:
+    int findKthLargest(vector<int>& nums, int k) {
+        priority_queue<int, vector<int>, greater<>> pq;
+        for(auto N : nums) {
+            pq.push(N);
+            if(pq.size() > k) {
+                pq.pop();
+            }
+        }
+        return pq.top();
+    }
+};
+```

solutions/heaps/sort-array-by-increasing-frequency.md

@@ -0,0 +1,38 @@
+## Sort Array By Increasing Frequency
+
+```cpp
+class Solution {
+public:
+    vector<int> frequencySort(vector<int>& nums) {
+        
+        unordered_map<int, int> cnt;
+        
+        for(int n : nums) cnt[n]++;
+        
+        auto cmp = [&](int a, int b) {
+            if(cnt[a] == cnt[b]) {
+                return a < b;
+            }
+            return cnt[a] > cnt[b];
+        };
+        priority_queue<int, vector<int>, decltype(cmp)> pq(cmp);
+        
+        for(auto &[n, c] : cnt) {
+            pq.push(n);
+        }
+        
+        vector<int> ans;
+        
+        while(pq.size()) {
+            int c = pq.top();
+            pq.pop();
+            
+            while(cnt[c]--) {
+              ans.push_back(c);  
+            }      
+        }
+        
+        return ans;
+    }
+};
+```

solutions/heaps/sort-characters-by-frequency.md

@@ -0,0 +1,33 @@
+## Sort Characters By Frequency
+
+```cpp
+class Solution {
+public:
+    string frequencySort(string s) {
+        
+        unordered_map<char, int> cnt;
+        
+        for(char c : s) {
+            cnt[c]++;
+        }
+        
+        auto cmp = [&](char a, char b) { return cnt[a] < cnt[b]; };
+        priority_queue<char, vector<char>, decltype(cmp)> pq(cmp);
+        
+        for(auto &[c, n] : cnt) {
+            pq.push(c);
+        }
+        
+        string ans = "";
+        
+        while(pq.size()) {
+            char c = pq.top();
+            pq.pop();
+            
+            ans += string(cnt[c], c);
+        }
+        
+        return ans;
+    }
+};
+```

solutions/heaps/top-k-frequent-elements.md

@@ -0,0 +1,35 @@
+## Top K Frequent Elements
+
+```cpp
+class Solution {
+public:
+    vector<int> topKFrequent(vector<int>& nums, int k) {
+        
+        unordered_map<int, int> cnt;
+        
+        auto cmp = [&](int a, int b) { return cnt[a] > cnt[b]; };
+        priority_queue<int, vector<int>, decltype(cmp)> pq(cmp);
+        
+        for(int n : nums) cnt[n]++;
+        
+        for(auto &[n, c] : cnt) {
+            pq.push(n);
+        }
+        
+        vector<int> ans;
+        
+        while(pq.size() > k) {
+            int c = pq.top();
+            pq.pop();
+        } 
+        
+        while(pq.size()) {
+            int c = pq.top();
+            pq.pop();
+            ans.push_back(c);
+        }
+        
+        return ans;
+    }
+};
+```