先來看個(gè)實(shí)例
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#!/usr/bin/env python import sys def search2(a,m): low = 0 high = len(a) - 1 while(low <= high): mid = (low + high)/2 midval = a[mid] if midval < m: low = mid + 1 elif midval > m: high = mid - 1 else: print mid return mid print -1 return -1 if __name__ == "__main__": a = [int(i) for i in list(sys.argv[1])] m = int(sys.argv[2]) search2(a,m) |
運(yùn)行:
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注:
1.'__'：由于python的類成員都是公有、公開的被存取public，缺少像正統(tǒng)面向?qū)ο笳Z言的私有private屬性。
于是就用__來將就一下，模擬私有屬性。這些__屬性往往是內(nèi)部使用，通常情況下不用改寫。也不用讀取。
加上2個(gè)下劃線的目的，一是不和普通公有屬性重名沖突，二是不讓對象的使用者(非開發(fā)者)隨意使用。
2.__name__ == "__main__"表示程序腳本是直接被執(zhí)行的.
如果不等于表示腳本是被其他程序用import引入的.則其__name__屬性被設(shè)為模塊名
Python采用二分查找找出數(shù)字的下標(biāo)
要考慮有重復(fù)數(shù)字的情況
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class Solution(object): def searchRange(self, nums, target): """ :type nums: List[int] :type target: int :rtype: List[int] """ def binary_search(start,end,value): while end>=start: mid = (start+end)//2 print(mid) if nums[mid]>target: end = mid-1 elif nums[mid]<target: start = mid+1 else: if value==-1: if mid-1>=start and nums[mid+value] == target: end = mid+value else: return mid else: if mid+1<=end and nums[mid+value] == target: start = mid+value else: return mid return -1 a=binary_search(0,len(nums)-1,-1) b=binary_search(0,len(nums)-1,1) return [a,b]a = Solution()l = [2,2]print(a.searchRange(l,2)) |
二分算法的定義不在多說了，百度一下就知道（支持國產(chǎn)大笑）
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import sys source = [1,2,3,4,5,6,7,8,9,10] #must be in order des = int(sys.argv[1]) low = 0high = len(source) - 1targetIndex = -1print "des=",des while low <= high: middle = (low + high)/2 if des == source[middle]: targetIndex = middle break elif des < source[middle]: high = middle -1 print "middle element[index=",middle,",value=",source[middle],"] is bigger than des, continue search from[",low,"to",high,"]" else: low = middle + 1 print "middle element[index=",middle,",value=",source[middle],"] is smaller than des, continue search from[",low,"to",high,"]"print "search complete, target element's index in source list is ",targetIndex |
最后在分享一個(gè)
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'fileName--BinarySearch.py' src = [] def BinarySearch(low, high, target, *src): '二分查找' while low <= high: mid = (low + high) // 2 midVal = src[mid] if target < midVal: high = mid - 1 elif target > midVal: low = mid + 1 else: return mid BinarySearch(low, high, target, *src) print('Please input 10 number:') for number in range(10): src.append(int(input('Num %d:' % number))) sortList = tuple(src) key = int(input('Please input key:')) location = BinarySearch(0, len(src) - 1, key, *sortList) if location != None: print('Find target at %d' % (location + 1)) else: print('No target!') |
