Find the number of zeroes | GeeksforGeeks

Given an array of 1s and 0s which has all 1s first followed by all 0s. Find the number of 0s. Count the number of zeroes in the given array.
Since the input array is sorted, we can use Binary Search to find the first occurrence of 0. Once we have index of first element, we can return count as n – index of first zero.

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;

}

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