Problem0033

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Published: Jan 8, 2018 License: MIT Imports: 0 Imported by: 0

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33. Search in Rotated Sorted Array

题目

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

解题思路

先假设old = [0, 1, 2, 4, 5, 6, 7],利用二分查找法,很容易可以5的索引号,当old变换成了new = [4, 5, 6, 7, 0, 1, 2]以后,同样可以使用二分查找法,因为old和new中的元素有明确的对应关系

old[i] == new[j],只要i和j满足关系式

j=i+4
if j > len(old) {
    j -= len(old)
}

其中,4 = old中的最大值在new中的索引号 + 1

所以,如果我们手中只有new,我们可以假装自己还是在对old使用二分查找法,当需要获取old[i]的值进行比较判断的时候,使用new[j]的值替代即可。

总结

本题是二分查找法的升级版

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