面试53题:
题目:统计一个数字在排序数组中出现的次数。
思路:二分查找法,分别找到此数字在排序数组中第一次和最后一次出现的位置,然后次数等于两个位置之差加1。
时间复杂度:O(log n)
解题思路一:
class Solution:
def GetNumberOfK(self, data, k):
number = 0
if data !=None and len(data)>0:
length=len(data)
first = self.GetFirst(data,length,k,0,length-1)
last = self.GetLast(data,length,k,0,length-1)
if first > -1 and last > -1:
number=last-first+1
return number
def GetFirst(self,data,lenth,k,start,end):
if start>end:
return -1
middle = (start+end)//2
if data[middle]==k:
if middle>0 and data[middle-1]==k:
end = middle -1
else:
return middle
elif data[middle]>k:
end=middle-1
else:
start=middle+1
return self.GetFirst(data,lenth,k,start,end)
def GetLast(self, data, lenth, k, start, end):
if start>end:
return -1
middle=(start+end)//2
if data[middle]==k:
if middle<end and data[middle+1]==k:
start = middle+1
else:
return middle
elif data[middle]>k:
end=middle-1
else:
start=middle+1
return self.GetLast(data, lenth, k, start, end)
解题思路二:标准库写法。
def searchRange(self, nums: List[int], target: int) -> List[int]:
from bisect import bisect, bisect_left
lo = bisect_left(nums, target)
if target in nums[lo:lo+1]:
return lo, bisect(nums, target)-1
else:
return -1, -1