Leetcode/702.SearchinaSortedArrayofUnknownSize.h at master · bluepp/Leetcode · GitHub

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/*
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: 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:

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].
*/

    int search(const ArrayReader& reader, int target) {
        int l = 0, r = INT_MAX;

        while (l < r) {
            int m = l + (r-l)/2;
            int x = reader.get(m);

            if (x == target) {
                return m;
            } else if (x < target) {
                l = m+1;
            } else {
                r = m;
            }
        }

        return -1;
    }