Smallest missing number

Given a sorted array of n distinct integers where each integer is in the range from 0 to m-1 and m > n.Find the smallest number that is missing from the array.

Examples :
Input: {0, 1, 2, 6, 9}, n = 5, m = 10
Output: 3

Discussion :

We will modify the standard Binary Search algorithm to compare the middle element with its index and make decision on the basis of this comparison.

int firstMissing(int array[], int start, int end){ 
    if (start > end) return end + 1; 
    if (start != array[start]) return start; 
    int mid = (start + end) / 2; 
    if (array[mid] == mid) return firstMissing(array, mid+1, end); 
    return firstMissing(array, start, mid); 
}