Question

702. 搜索长度未知的有序数组

English Version

题目描述

这是一个交互问题。

您有一个升序整数数组，其长度未知。您没有访问数组的权限，但是可以使用 ArrayReader 接口访问它。你可以调用 ArrayReader.get(i):

• 返回数组第ith个索引(0-indexed)处的值(即secret[i])，或者

• 如果 i  超出了数组的边界，则返回 231 - 1

你也会得到一个整数 target。

如果存在secret[k] == target，请返回索引 k 的值；否则返回 -1

你必须写一个时间复杂度为 O(log n) 的算法。

 

示例 1：

输入: secret = [-1,0,3,5,9,12], target = 9
输出: 4
解释: 9 存在在 nums 中，下标为 4

示例 2：

输入: secret = [-1,0,3,5,9,12], target = 2
输出: -1
解释: 2 不在数组中所以返回 -1

 

提示：

• 1 <= secret.length <= 104
• -104 <= secret[i], target <= 104
• secret 严格递增

解法

方法一

# """
# This is ArrayReader's API interface.
# You should not implement it, or speculate about its implementation
# """
# class ArrayReader:
#  def get(self, index: int) -> int:


class Solution:
  def search(self, reader, target):
    """
    :type reader: ArrayReader
    :type target: int
    :rtype: int
    """
    left, right = 0, 20000
    while left < right:
      mid = (left + right) >> 1
      if reader.get(mid) >= target:
        right = mid
      else:
        left = mid + 1
    return left if reader.get(left) == target else -1

/**
 * // 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 left = 0, right = 20000;
    while (left < right) {
      int mid = left + right >> 1;
      if (reader.get(mid) >= target) {
        right = mid;
      } else {
        left = mid + 1;
      }
    }
    return reader.get(left) == target ? left : -1;
  }
}

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

class Solution {
public:
  int search(const ArrayReader& reader, int target) {
    int left = 0, right = 20000;
    while (left < right) {
      int mid = left + right >> 1;
      if (reader.get(mid) >= target) {
        right = mid;
      } else {
        left = mid + 1;
      }
    }
    return reader.get(left) == target ? left : -1;
  }
};

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

func search(reader ArrayReader, target int) int {
  left, right := 0, 20000
  for left < right {
    mid := (left + right) >> 1
    if reader.get(mid) >= target {
      right = mid
    } else {
      left = mid + 1
    }
  }
  if reader.get(left) == target {
    return left
  }
  return -1
}