QuickSelect implementation

quickSelect.cpp

#include <bits/stdc++.h>
using namespace std;

int randGen (int i) {srand(time(0)); return rand()%i;}

int partition(int A[], int lo, int hi)
{
    int pivot = A[hi];
    int i = lo-1;
    for (int j=lo; j<=hi; j++)
    {
        if (A[j]>pivot) continue;
        i ++;
        int temp = A[i];
        A[i] = A[j];
        A[j] = temp;
    }
    return i;
}

int quickSelect(int A[], int lo, int hi, int K)
{
  if (K<1 || K>hi-lo+1) return -1;
  int pi = partition(A, lo, hi);
  if (pi-lo+1 == K) return A[pi];
  else if (pi-lo+1 < K) return quickSelect(A, pi+1, hi, K-pi+lo-1);
  return quickSelect(A, lo, pi-1, K);
}

int main()
{
    int A[] = {1,2,3,4,5,6,7};
    int n = sizeof(A)/sizeof(int);
    random_shuffle(A, A+n, randGen);
    cout << "   Input:";
    for (int i=0; i<n; i++)cout<<A[i]<<','; cout<<endl;
    int kth_element = quickSelect(A, 0, n-1, 3);
    cout << "  Output:";
    for (int i=0; i<n; i++)cout<<A[i]<<','; cout<<endl;
    cout<< " 3rd item:"<<kth_element<<endl;
    return 0;
}