1. lower_bound(nums, target)
在非遞減數組nums中,lower_bound(nums, target)返回第一個大於等於target的值得位置,如果nums中元素均小於target(即不存在>=target的元素),則返回nums的長度(即target如果要插入到nums中,應該插入的位置)
#coding=utf-8
#返回nums中第一個>=target的值得位置,如果nums中都比target小,則返回len(nums)
def lower_bound(nums, target):
low, high = 0, len(nums)-1
pos = len(nums)
while low<high:
mid = (low+high)/2
if nums[mid] < target:
low = mid+1
else:#>=
high = mid
pos = high
return pos
測試:
nums = [10, 10, 10, 20, 20, 20, 30, 30]
print lower_bound(nums, 9),
print lower_bound(nums, 10),
print lower_bound(nums, 15),
print lower_bound(nums, 20),
print lower_bound(nums, 25),
print lower_bound(nums, 30),
print lower_bound(nums, 40)
運行結果:
2. upper_bound(nums, target)
在非遞減數組nums中,upper_bound(nums, target)返回第一個大於target的值的位置,如果nums中元素均小於等於target(即不存在>target的元素),則返回nums的長度(即target如果要插入到nums中,應該插入的位置)
#返回nums中第一個>target的值得位置,如果nums中都不比target大,則返回len(nums)
def upper_bound(nums, target):
low, high = 0, len(nums)-1
pos = len(nums)
while low<high:
mid=(low+high)/2
if nums[mid]<=target:
low = mid+1
else:#>
high = mid
pos = high
return pos
測試:
nums = [10, 10, 10, 20, 20, 20, 30, 30]
print upper_bound(nums, 9),
print upper_bound(nums, 10),
print upper_bound(nums, 15),
print upper_bound(nums, 20),
print upper_bound(nums, 25),
print upper_bound(nums, 30),
print upper_bound(nums, 40)
運行結果:
c++ lower_bound源碼參考:http://www.cplusplus.com/reference/algorithm/lower_bound/
c++ upper_bound源碼參考:http://www.cplusplus.com/reference/algorithm/upper_bound/