降序
构建最小堆
#include <iostream>
using namespace std;
const int N = 1e5 + 10;
int arr[N];
void adjust(int a[], int n, int i){
int mi = i, l = i * 2 + 1, r = i * 2 + 2;
if(l < n && a[mi] > a[l]) mi = l;
if(r < n && a[mi] > a[r]) mi = r;
if(mi != i){
swap(a[mi], a[i]);
adjust(a, n, mi);
}
}
void buildMinHeap(int a[], int n){
for(int i = n / 2 - 1; i >= 0; i--){
adjust(a, n, i);
}
for(int i = n - 1; i >= 0; i--){
swap(a[0], a[i]);
adjust(a, i, 0);
}
}
int main(){
int n;
cin >> n;
for(int i = 0; i < n; i++) cin >> arr[i];
buildMinHeap(arr, n);
return 0;
}
升序
构建最大堆
#include <iostream>
using namespace std;
const int N = 1e5 + 10;
int arr[N];
void adjust(int a[], int n, int i){
int ma = i, l = i * 2 + 1, r = i * 2 + 2;
if(l < n && a[ma] < a[l]) ma = l;
if(r < n && a[ma] < a[r]) ma = r;
if(ma != i){
swap(a[ma], a[i]);
adjust(a, n, ma);
}
}
void buildMinHeap(int a[], int n){
for(int i = n / 2 - 1; i >= 0; i--){
adjust(a, n, i);
}
for(int i = n - 1; i >= 0; i--){
swap(a[0], a[i]);
adjust(a, i, 0);
}
}
int main(){
int n;
cin >> n;
for(int i = 0; i < n; i++) cin >> arr[i];
buildMinHeap(arr, n);
return 0;
}