heap sort added

Author: arorarahul

README.md

@@ -177,7 +177,8 @@ For eg storing the minimum so far in another stack so that each time when a numb
 ### Heaps
 
 - [Given an array, create a max heap](/heaps/question1.c)
-- [Given a max heap, apply different heap operations (find max, delete max,increase key, insert key, decrease key.)](/heaps/question1.c)
+- [Given a max heap, apply different heap operations (find max, delete max,increase key, insert key, decrease key.)](/heaps/question2.c)
+- [Write a program for heap sort](/heaps/question3.c)
 
 ## Some important concepts to solve algos better
 

heaps/question3.c

@@ -0,0 +1,59 @@
+/*
+Program to write heap sort
+
+Time complexity: O(nlogn)
+because max heapify is called n times and for nearly n/2 times the height of the tree remains same (maximum),
+therefore here it will be nlogn only
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void maxHeapify(int arr[],int i,int size){
+	if(size < 1){
+		return;
+	}
+	int left = 2*i+1,right=2*i+2,largest, temp, heapSize = size;
+	if(left <= heapSize-1 && arr[left] > arr[i]){
+		largest = left;
+	}else{
+		largest = i;
+	}
+	if(right <= heapSize-1 && arr[right] > arr[largest]){
+		largest = right;
+	}
+	
+	if(largest <= heapSize-1 && largest != i){
+		temp = arr[largest];
+		arr[largest] = arr[i];
+		arr[i]=temp;
+		maxHeapify(arr,largest,size);
+	}
+}
+
+void display(int arr[],int size){
+	for(int i=0;i<size;i++){
+		printf("%d\t", arr[i]);
+	}
+	printf("\n");
+}
+
+void heapSort(int arr[], int size){
+	int temp;
+	for(int i=size-1;i>=1;i--){
+		temp = arr[0];
+		arr[0] = arr[i];
+		arr[i]=temp;
+		maxHeapify(arr,0,i);
+	}
+	display(arr,size);
+}
+
+int main(){
+	int heap[] = {100,20,30,10,15,7,16};
+	int size = sizeof(heap)/sizeof(heap[0]);
+
+	heapSort(heap,size);
+
+	return 0;
+}