[Algo] 20. Search In Unknown Sized Sorted Array

Given a integer dictionary A of unknown size, where the numbers in the dictionary are sorted in ascending order, determine if a given target integer T is in the dictionary. Return the index of T in A, return -1 if T is not in A.

Assumptions

• dictionary A is not null
• dictionary.get(i) will return null(Java)/INT_MIN(C++)/None(Python) if index i is out of bounds

Examples

• A = {1, 2, 5, 9, ......}, T = 5, return 2
• A = {1, 2, 5, 9, 12, ......}, T = 7, return -1

/*
*  interface Dictionary {
*    public Integer get(int index);
*  }
*/

// You do not need to implement the Dictionary interface.
// You can use it directly, the implementation is provided when testing your solution.
public class Solution {
  public int search(Dictionary dict, int target) {
    // Write your solution here
    int start = 0;
    int end = 1;
    while (dict.get(end) != null && dict.get(end) <= target) {
      start = end;
      end = 2 * end;
    }

    while (start <= end) {
      int mid = start + (end - start) / 2;
      if (dict.get(mid) == null || dict.get(mid) > target) {
        end = mid - 1;
      } else if (dict.get(mid) < target) {
        start = mid + 1;
      } else {
        return mid;
      }
    }
    return -1;
  }
}