702. Search in a Sorted Array of Unknown Size

Description

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.

Constraints

• 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].

• The length of the array will be in the range [1, 10^4].

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

/**
 * // This is ArrayReader's API interface.
 * // You should not implement it, or speculate about its implementation
 * interface ArrayReader {
 *     public int get(int index) {}
 * }
 */

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

Solution 2

/**
 * Time complexity : 
 * Space complexity : 
 */

/**
 * // This is ArrayReader's API interface.
 * // You should not implement it, or speculate about its implementation
 * interface ArrayReader {
 *     public int get(int index) {}
 * }
 */

class Solution {
    public int search(ArrayReader reader, int target) {
        int high = 1;
        while(reader.get(high) < target) {
            high *= 2;
        }
        
        int low = high / 2;
        
        while(low <= high) {
            int mid = low + (high-low)/2;
            int val = reader.get(mid);
            if(val == target) {
                return mid;
            } else if(val < target) {
                low = mid+1;
            } else {
                high = mid-1;
            }
        }
        return -1;
    }
}

Follow up