Knowledge points
Maximum heap: for all nodes i, the key value is less than or equal to the key value of the parent node
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Question content
For sequence A, the maximum heap is realized by using the property of the maximum heap
thinking
For A sequence A containing n elements. i starts from n/2 and traverses at 1. Each execution of maxHeapify is A comparison between the left and right nodes. If it is larger than the child node, it will be exchanged until it cannot be compared.
Code
Realize the function of maximum heap
#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
const int maxx = 2000000;
int A[maxx + 1];
int n;
void maxHeapify(int i) {
int left = 2 * i, right = 2 * i + 1;
int largest;
// Select the node with the largest value from the left sub node, self and right sub node, and continue to recurse
if (left <= n && A[left] > A[i])
largest = left;
else
largest = i;
if (right <= n && A[right] > A[largest])
largest = right;
if (largest != i) {
swap(A[i], A[largest]);
maxHeapify(largest);
}
}
int main()
{
scanf("%d", &n);
for (int i = 1; i <= n; i++)
scanf("%d", &A[i]);
for (int i = n / 2; i >= 1; i--)
maxHeapify(i);
for (int i = 1; i <= n; i++)
printf(" %d", A[i]);
printf("\n");
return 0;
}Using vector and make'heap() of STL
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;
const int maxx = 200000;
int main()
{
int n, k;
vector<int> ve;
scanf("%d", &n);
for (int i = 1; i <= n; i++) {
scanf("%d", &k);
ve.push_back(k);
}
make_heap(ve.begin(), ve.end());
for (vector<int>::iterator it = ve.begin(); it != ve.end(); it++)
printf(" %d", *it);
printf("\n");
return 0;
}