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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

二分法。

Python3

# """
# 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

Java

/**
 * // 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;
    }
}

C++

/**
 * // 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;
    }
};

Go

/**
 * // 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
}

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