702-search-in-a-sorted-array-of-unknown-size

Question

https://leetcode.com/problems/search-in-a-sorted-array-of-unknown-size/description/

Given an integer array sorted in ascending order, write a function to searchtargetinnums. Iftargetexists, then return its index, otherwise return-1.However, the array size is unknown to you. You may only access the array using anArrayReader interface, where ArrayReader.get(k)returns the element of the array at indexk (0-indexed).

You may assume all integers in the array are less than 10000, and if you access the array out of bounds,ArrayReader.getwill return2147483647.

Example 1:

Input: array = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: array = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Note:

1. You may assume that all elements in the array are unique.
2. The value of each element in the array will be in the range [-9999, 9999].

Thought Process

1. Binary Search
   1. We set our search index to be from 0 to 2147483647, named lo and hi
   2. Our search ends when we hit our target or hi > lo
   3. Time complexity O(1) from 32 times or search
   4. Space complexity O(1)

Solution

class Solution {
    public int search(ArrayReader reader, int target) {
        int lo = 0, hi = Integer.MAX_VALUE;
        while (lo <= hi) {
            int mi = lo + (hi - lo) / 2;
            int val = reader.get(mi);
            if (val == target) return mi;
            else if (val < target) lo = mi + 1;
            else hi = mi - 1;
        }
        return -1;
    }
}

Additional