c_cpp 流中的第k个最大元素

Posted 2021-05-14

// https://www.geeksforgeeks.org/kth-largest-element-in-a-stream/
#include <iostream>
using namespace std;

void MaxHeapify(int a[], int n, int i) {
    int l= 2*i+1, r= 2*i+2, largest = i;
    if (l<n) {
        if (a[l] > a[largest])
            largest= l;
        if (r<n && a[r] > a[largest])
            largest = r;
        if (largest != i) {
            swap (a[i], a[largest]);
            MaxHeapify(a, n, largest);
        }
    }
}

int extractMax(int b[], int n, int k) {
    int s;
    for (int i=0; i<k; i++) {
        s=b[0];
        b[0]=b[n-1-i];
        MaxHeapify(b, n-i, 0);
    }
    return s;
}

void kLargest (int a[], int n, int k) {
    for (int i=0; i<k-1;i++)
        cout<< -1 << " ";

    for (int i=k-1; i<n; i++) {
        int b[i+1];
        copy (a, a+i+1, b); //keep cropping the array and find the kth largest element in the resultant array.

        for (int j= (i-1)/2; j>=0; j--) //Create the Max Heap from the resultant array to use it in extract min
            MaxHeapify(b, i+1, j);

        int s = extractMax(b,i+1,k);
        cout<< s <<  " ";
    }
}

int main() {
    int t;
    cin>>t;
    while (t-->0) {
        int n, k;
        cin>> k>> n;
        int a[n];
        for (int i=0; i<n; i++)
            cin>> a[i];
        kLargest (a, n, k);
        cout<< "\n";
    }
}