Formatted question description: https://leetcode.ca/all/702.html

702. Search in a Sorted Array of Unknown Size (Medium)

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:

  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].

Companies:
Google

Related Topics:
Binary Search

Similar Questions:

Solution 1.

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

// Time: O(1)
// Space: O(1)
class Solution {
public:
    int search(const ArrayReader& reader, int target) {
        int minVal = reader.get(0);
        int L = 0, R = 9999 - minVal;
        while (L <= R) {
            int M = (L + R) / 2;
            int val = reader.get(M);
            if (val == target) return M;
            if (val > target) R = M - 1;
            else L = M + 1;
        }
        return -1;
    }
};

Solution 2.

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

// Time: O(1)
// Space: O(1)
// Ref: https://leetcode.com/problems/search-in-a-sorted-array-of-unknown-size/discuss/151685/Shortest-and-cleanest-Java-solution-so-far
class Solution {
public:
    int search(const ArrayReader& reader, int target) {
        int L, R = 1;
        while (reader.get(R) < target) R *= 2;
        L = R / 2;
        while (L <= R) {
            int M = (L + R) / 2;
            int val = reader.get(M);
            if (val == target) return M;
            if (val > target) R = M - 1;
            else L = M + 1;
        }
        return -1;
    }
};

Java

class Solution {
    public int search(ArrayReader reader, int target) {
        if (reader.get(0) == target)
            return 0;
        int low = 0, high = 1;
        while (reader.get(high) < target) {
            low = high + 1;
            high <<= 1;
        }
        while (low <= high) {
            int mid = ((high - low) >> 1) + low;
            int num = reader.get(mid);
            if (num == target)
                return mid;
            else if (num > target)
                high--;
            else
                low++;
        }
        return -1;
    }
}

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