Python|包含正整数和负整数的列表中的计数符号变化
给定一个包含正整数和负整数的列表，我们必须找出列表中符号（正或负）变化的次数。
Input: [-1, 2, 3, -4, 5, -6, 7, 8, -9, 10, -11, 12]
Output:9
Explanation :
Sign change from -1 to 2, ans = 1
Sign change from 3 to -4, ans = 2
Sign change from -4 to 5, ans = 3
Sign change from 5 to -6, ans = 4
Sign change from -6 to 7, ans = 5
Sign change from 8 to -9, ans = 6
Sign change from -9 to 10, ans = 7
Sign change from 10 to -11 ans = 8
Sign change from -11 to 12, ans = 9
Input: [-1, 2, 3, -4, 5, -11, 12]
Output:5
Explanation :
Sign change from -1 to 2, ans = 1
Sign change from 3 to -4, ans = 2
Sign change from -4 to 5, ans = 3
Sign change from 5 to -11, ans = 4
Sign change from -11 to 12, ans = 5
让我们讨论执行此任务的某些方式。
方法#1：使用迭代
使用迭代查找列表中时间符号更改的数量。
# Python Code to find number of
# time sign changes in the list.
# Input list Initialization
Input = [-1, 2, 3, -4, 5, -6, 7, 8, -9, 10, -11, 12]
# Variable Initialization
prev = Input[0]
ans = 0
# Using Iteration
for elem in Input:
if elem == 0:
sign = -1
else:
sign = elem / abs(elem)
if sign == -prev:
ans = ans + 1
prev = sign
# Printing answer
print(ans)
输出 ：
9方法 #2：使用 Itertools 和 groupby
这是使用 itertools 执行此特定任务的另一种方法。
# Python Code to find number of
# time sign changes in the list.
# Input list Initialization
Input = [-1, 2, 3, -4, 5, -6, 7, 8, -9, 10, -11, 12]
# Importing
import itertools
# Using groupby
Output = len(list(itertools.groupby(Input, lambda Input: Input > 0)))
Output = Output -1
# Printing output
print(Output)
输出 ：
9方法 #3：使用 Zip
在列表中查找时间符号更改次数的最简洁易读的方法是使用 zip。
# Python Code to find number of
# time sign changes in the list.
# Using zip to check
def check(Input):
Input = [-1 if not x else x for x in Input]
# zip with leading 1, so that opening negative value is
# treated as sign change
return sum((x ^ y)<0 for x, y in zip([1]+Input, Input))
# Input list Initialization
Input = [-1, 2, 3, -4, 5, -6, 7, 8, -9, 10, -11, 12]
Output = check(Input)
Output = Output -1
# Printing output
print(Output)
输出 ：
9