Merge pull request #11 from Stormbreakerr20/Contributing

Created Application Folder #5

Computational_Algorithms/Heaps/heapify.cpp

@@ -0,0 +1,42 @@
+// an array will  be given to you which is not a heap
+
+// heapify function is used to put the given node of bt to its correct position so it follows order of max heap
+
+// for given array we know leaf node are from n/2+1 to n : hence those nodes are alrady a heap individually so we need to solve for 1 to n/2
+
+// if we start indexing from 0 : left =2i+1 right = 2i+2
+
+#include<iostream>
+using namespace std;
+// O(logn)
+void heapify(int *arr , int n, int i){
+    int leftchild = 2*i;
+    int rightchild = 2*i +1;
+    int largest=i;
+
+    if(leftchild<n && arr[leftchild]>arr[largest]){
+        largest=leftchild;
+    }
+    else if(rightchild<n && arr[rightchild]>arr[largest]){
+        largest=rightchild;
+    }
+
+    if(largest!=i){
+        swap(arr[largest],arr[i]);
+        heapify(arr,n,largest);
+    }
+}
+
+int main(){
+    int arr[6]={-1,54,55,53,52,50};
+    int n=5;
+    // build heap : O(n)
+    // if arr started directly from 0th index the i =n/2 -1 where n=arr.size() as leaf node found at arr.size()/2 to arr.size()-1
+    for(int i=n/2 ; i>0 ;i--){
+        heapify(arr,n,i);
+    }
+
+    for(int i=1 ; i<=n ;i++){
+        cout<<arr[i]<<" ";
+    }
+}