SearchInInfiniteArray.java

package Leetcode;

/**
 * @author kalpak
 *
 * 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
 *
 * 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].
 */

class ArrayReader {
 int[] arr;

 ArrayReader(int[] arr) {
 this.arr = arr;
 }

 public int get(int index) {
 if (index >= arr.length)
 return Integer.MAX_VALUE;
 return arr[index];
 }
}

public class SearchInInfiniteArray {
 public static int search(ArrayReader reader, int target) {
 int left = 0;
 int right = 1;

 while(reader.get(right) < target)
 right *= 2;

 while(left <= right) {
 int mid = left + (right - left)/2;

 if(target == reader.get(mid))
 return mid;

 if(reader.get(mid) < target)
 left = mid + 1;
 else
 right = mid - 1;
 }
 return -1;
 }

 public static void main(String[] args) {
 ArrayReader reader = new ArrayReader(new int[] { 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 });
 System.out.println(search(reader, 14));
 }
}