number of zeros number of ones in an array algorithm code example

Example: count number of zeros in array in O(logN)

int firstZero(int arr[], int low, int high) 
{
	if (high >= low) 
    { 
        // Check if mid element is first 0 
        int mid = low + (high - low)/2; 
        if (( mid == 0 || arr[mid-1] == 1) && arr[mid] == 0) 
            return mid; 
        if (arr[mid] == 1)  // If mid element is not 0 
            return firstZero(arr, (mid + 1), high); 
        else  // If mid element is 0, but not first 0 
            return firstZero(arr, low, (mid -1)); 
    } 
    return -1; 
}   
// A wrapper over recursive function firstZero() 
int countZeroes(int arr[], int n) 
{ 
    // Find index of first zero in given array 
    int first = firstZero(arr, 0, n-1); 
    // If 0 is not present at all, return 0 
    if (first == -1) 
        return 0; 
    return (n - first); 
} 

//Credits : GeeksForGeeks