Binary search with bug or inaccuracy - c++

Question

First of all, sorry for my English.
I am solving this problem:
Tom wants to shoot from a cannon at the Jerry, but he would like to have as many pieces as possible, but they must be the same size and as big as possible too. He only have n cannonballs at his disposal, so he can cut them in smaller pieces. And he would like to have k + 1 pieces to shoot from cannon at the Jerry. He knows the radius of every cannonball. What is the biggest volume of one piece? Output is rounded printf("%.3f\n",answer). First number is n and the second k , next n numbers are radiuses of cannonballs.
Possible input:
3 50
1 2 3
Output: 2.900*
Here is my solution: The volume of every piece can be only smaller or equal to volume of the smallest cannonball because you cannot join parts from cannonballs together. So I have used Binary search from 0.0 to minimal volume and as the predicate I have used function numberOfPieces, which counts the number of pieces from every cannonball with specific volume of one piece(this is the median in binary search). This function return number of pieces I can get if I use median as volume of one piece. Then I just compare it to k + 1 and if it is bigger or equal I use median as low otherwise I use it as high. My solution works for this test input.
The problem is that I get WA(wrong answer) and I cannot check the test input values. Can you please look at my code and check if I did something wrong please? The problem may be number inaccuracy, but I have small EPS so it should be good. Thanks in advance for every idea.
Here is my code:
#include <vector>
#include <iostream>
#include <algorithm>
#include <stdio.h>
#define PI 3.14159265358979323846
#define VC ((4.0/3.0) * PI) // constant for volume calculation
#define EPS 1E-12
using namespace std;
// return the number of pieces depending on the volume
int numberOfPieces(int v[], int n, double volume)
{
int ans = 0;
for(int i = 0; i < n; i++)
ans += (int)(v[i] * VC / volume);
return ans;
}
double binarySearch(double a, double b, int k, int n, int v[])
{
double low = a, high = b;
while(abs(low-high) > EPS)
{
double mid = low + (high - low) / 2.0;
if(numberOfPieces(v, n, mid) >= k)
low = mid;
else
high = mid;
}
return (low + high)/2.0;
}
int main()
{
int n, k, x; // n - number of cannonballs, k - number of wanted pieces, x - variable for input
int v[10001]; // radiuses ^ 3 of the cannonballs
scanf("%d%d", &n, &k);
int minVolume = 9999999;
for(int i = 0; i < n; i++) {
scanf("%d",&x);
minVolume = min(minVolume, x);
v[i] = x * x * x;
}
printf("%.3f\n", binarySearch(0.0, minVolume * minVolume * minVolume * VC, k + 1, n, v));
return 0;
}

Answer 1

The problem was I was setting minimal volume as high in the binary search, but I should use the maximal volume. The second problem was I was not passing maximal radius ^ 3 to the binary search function. Thanks for help