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Problem
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 = 9Output: 4Explanation: 9 exists in nums and its index is 4Example 2:
Input: array = [-1,0,3,5,9,12], target = 2Output: -1Explanation: 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].
Solution
class Solution {
public int search(ArrayReader reader, int target) {
//find higher bound
int r = 1;
while (reader.get(r) < target) r *= 2;
//then you know lower bound
int l = r/2;
while (l <= r) {
int m = l+(r-l)/2;
if (reader.get(m) == target) return m;
else if (reader.get(m) < target) l = m+1;
else r = m-1;
}
return -1;
}
}