Problem:
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Maximum Heap

A binary heap which satisfies max-heap property is called max-heap. In a max-heap, for every node $i$ other than the root, $A[i] \leq A[parent(i)]$, that is, the value of a node is at most the value of its parent. The largest element in a max-heap is stored at the root, and the subtree rooted at a node contains values no larger than that contained at the node itself.

Here is an example of a max-heap.

Write a program which reads an array and constructs a max-heap from the array based on the following pseudo code.

$maxHeapify(A, i)$ move the value of $A[i]$ down to leaves to make a sub-tree of node $i$ a max-heap. Here, $H$ is the size of the heap.

1 maxHeapify(A, i)
2 l = left(i)
3 r = right(i)
4 // select the node which has the maximum value
5 if l ≤ H and A[l] > A[i]
6 largest = l
7 else
8 largest = i
9 if r ≤ H and A[r] > A[largest]
10 largest = r
11
12 if largest ≠ i　// value of children is larger than that of i
13 swap A[i] and A[largest]
14 maxHeapify(A, largest) // call recursively

The following procedure buildMaxHeap(A) makes $A$ a max-heap by performing maxHeapify in a bottom-up manner.

1 buildMaxHeap(A)
2 for i = H/2 downto 1
3 maxHeapify(A, i)

Input

In the first line, an integer $H$ is given. In the second line, $H$ integers which represent elements in the binary heap are given in order of node id (from $1$ to $H$).

Output

Print values of nodes in the max-heap in order of their id (from $1$ to $H$). Print a single space character before each value.

Constraint

$1 \leq H \leq 500,000$

$-2,000,000,000 \leq$ value of a node $\leq 2,000,000,000$

Sample Input 1

10
4 1 3 2 16 9 10 14 8 7

Sample Output 1

16 14 10 8 7 9 3 2 4 1

Reference

Introduction to Algorithms, Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein. The MIT Press.

Solution in C (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>

#define MAX 500001
#define NIL -2000000001

void maxHeapify(int*,int);
void buildMaxHeap(int*);

int H;

int main(){
    int key[MAX];
    int i;

    for(i = 0;i < MAX;i++){
        key[i] = NIL;
    }

    scanf("%d",&H);

    for(i = 1;i <= H;i++){
        scanf("%d",&key[i]);
    }

    buildMaxHeap(key);

    for(i = 1;i <= H;i++){
        printf(" %d",key[i]);
    }
    printf("\n");

    return 0;
}

void maxHeapify(int *A,int i){
    int largest,l,r;
    int tmp;

    l = i * 2;
    r = i * 2 + 1;

    if(l <= H && A[l] > A[i]){
        largest = l;
    }
    else{
        largest = i;
    }
    if(r <= H && A[r] > A[largest]){
        largest = r;
    }
    
    if(largest != i){
        tmp = A[i];
        A[i] = A[largest];
        A[largest] = tmp;
        maxHeapify(A,largest);
    }
}

void buildMaxHeap(int *A){
    int i;
    for(i = H / 2 ;i > 0;i--){
        maxHeapify(A,i);
    }
}