[Leetcode][Python]33: Search in Rotated Sorted Array
# -*- coding: utf8 -*-
'''
__author__ = 'dabay.wang@gmail.com' 33: Search in Rotated Sorted Array
https://oj.leetcode.com/problems/search-in-rotated-sorted-array/ Suppose a sorted array 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. ===Comments by Dabay===
解法一:(可以过OJ)
首先判断是否应该从前往后,还是从后往前。
取决于和第一个数的判断,如果比第一个数小,就从后往前;如果比第一个数大,就从前往后。
注意一些继续循环的条件:
从前往后的时候:下标有效、递增、目标比上一个大
从后往前的时候:下标有效、递减、目标比上一个小 解法二:(二分查找)
把中位数标记出来。
如果中位数比左边大,说明左边是递增的,断点在右边:
如果target在左边递增的区间,就在左边查找;
否则,在右边查找
如果中位数比左边小,说明右边是递增的,断点在左边:
如果target在右边的递增区间,就在右边查找;
否则,在左边查找。 从跑的结果来看,对于小数据来说,解法一速度还快一点点。
''' class Solution:
# @param A, a list of integers
# @param target, an integer to be searched
# @return an integer
def search(self, A, target):
left, right = 0, len(A)-1
while left <= right:
if A[left] == target:
return left
if A[right] == target:
return right
m = (left + right) / 2
mid = A[m]
if mid == target:
return m
if mid > A[left]:
if A[left]< target and target < A[m]:
right = m - 1
else:
left = m + 1
else:
if A[m] < target and target < A[right]:
left = m + 1
else:
right = m - 1
else:
return -1 # def search(self, A, target):
# if len(A) == 1:
# return [-1, 0][A[0]==target]
#
# if A[0] == target:
# return 0
# elif A[0] < target:
# i = 1
# while i < len(A) and A[i-1] < A[i] and A[i-1] < target:
# if A[i] == target:
# return i
# i = i + 1
# else:
# return -1
# else:
# if A[-1] == target:
# return len(A) - 1
# i = len(A) - 2
# while i >= 0 and A[i] < A[i+1] and target < A[i+1]:
# if A[i] == target:
# return i
# i = i - 1
# else:
# return -1 def main():
s = Solution()
nums = [4,5,6,7,8,1,2,3]
print s.search(nums, 8) if __name__ == "__main__":
import time
start = time.clock()
main()
print "%s sec" % (time.clock() - start)
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