Problem

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

You may assume all integers in the array are less than 10000, and if you access the array out of bounds, ArrayReader.get will return 2147483647.

Example 1:

Input: array = [-1,0,3,5,9,12], target = 9

Output: 4Explanation: 9 exists in nums and its index is 4Example 2:

Input: array = [-1,0,3,5,9,12], target = 2

Output: -1Explanation: 2 does not exist in nums so return -1

Note:

You may assume that all elements in the array are unique.

The value of each element in the array will be in the range [-9999, 9999].

Solution

class Solution {    public int search(ArrayReader reader, int target) {        //find higher bound        int r = 1;        while (reader.get(r) < target) r *= 2;        //then you know lower bound        int l = r/2;        while (l <= r) {            int m = l+(r-l)/2;            if (reader.get(m) == target) return m;            else if (reader.get(m) < target) l = m+1;            else r = m-1;        }        return -1;    }}