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  • 702. Search in a Sorted Array of Unknown Size

    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].

    先向外binary search找到右边界right,再向内binary search

    time: O(log_2(n)), space: O(1)

    class Solution {
        public int search(ArrayReader reader, int target) {
            int left = 0, right = 1;
            while(reader.get(right) != 2147483647) {
                right *= 2;
            }
            
            while(left <= right) {
                int mid = left + (right - left) / 2;
                if(reader.get(mid) == target)
                    return mid;
                else if(reader.get(mid) > target)
                    right = mid - 1;
                else
                    left = mid + 1;
            }
            return -1;
        }
    }
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  • 原文地址:https://www.cnblogs.com/fatttcat/p/10131182.html
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