README.md

702. 搜索长度未知的有序数组

English Version

题目描述

给定一个升序整数数组，写一个函数搜索 nums 中数字 target。如果 target 存在，返回它的下标，否则返回 -1。注意，这个数组的大小是未知的。你只可以通过 ArrayReader 接口访问这个数组，ArrayReader.get(k) 返回数组中第 k 个元素（下标从 0 开始）。

你可以认为数组中所有的整数都小于 10000。如果你访问数组越界，ArrayReader.get 会返回 2147483647。

 

样例 1：

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

样例 2：

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

 

注释 ：

1. 你可以认为数组中所有元素的值互不相同。
2. 数组元素的值域是 [-9999, 9999]。

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
}

...