打印所有大于其左邻居的整数

Question

（使用python 3）这是我被赋予的任务：

给定一个数字列表，找到并打印其所有大于其左邻居的元素。

示例输入

1 5 2 4 3

示例输出

5 4

这是我的代码：

# creates a list out of the input given as '# # # # # #...'
a = [int(s) for s in input().split()]

for i in a[1:]:               #skips the first since it has no "left neighbor"
   if i > a[a.index(i) - 1]:  #checks if 'i' is greater than element before 'i'
      print(i, end=' ')

我的问题是它适用于我所做的所有测试，除非我给它一个列表，a[0] == a[-1] 然后它会忽略列表中等于该整数的所有元素。

例如：

3 5 2 3 1 2 3 1 3
--> 5    

我一直很难找到错误！如果这个问题没有很好地提出，请原谅。这是我第一次在 stackoverflow 上提问。

Answer 1

试试这个：

for i in range(1, len(a)):
    if a[i] > a[i-1]:
        print(a[i], end=' ')

结果：

3 5 2 3 1 2 3 1 3
--> 5 3 2 3 3

Answer 2

使用filter 和lambda：

lst = [3, 5, 2, 3, 1, 2, 3, 1, 3]

greater = [item[1] for item in filter(lambda x: x[1] > x[0], zip(lst, lst[1:]))]
print(greater)

产量

[5, 3, 2, 3, 3]

或者，作为@Roadrunner cmets（我的最爱！）：

[y for x, y in zip(lst, lst[1:]) if y > x]

为了迷惑大众，你也可以编写自己的生成器函数：

def greater(iterable):
    ilst = iter(iterable)
    prev, current = None, next(ilst)
    while (ilst):
        if prev and current > prev:
            yield current
        prev, current = current, next(ilst)

greater_n = [g for g in greater(lst)]
print(greater_n)

---

计时（每次 100.000 次）：

def mushif():
    lst = [3, 5, 2, 3, 1, 2, 3, 1, 3]
    greater = []
    for i in range(1, len(lst)):
        if lst[i] > lst[i-1]:
            greater.append(lst[i])

def jan():
    lst = [3, 5, 2, 3, 1, 2, 3, 1, 3]
    greater = [item[1] for item in filter(lambda x: x[1] > x[0], zip(lst, lst[1:]))]


def roadrunner():
    lst = [3, 5, 2, 3, 1, 2, 3, 1, 3]
    greater = [y for x, y in zip(lst, lst[1:]) if y > x]

import timeit

print(timeit.timeit(mushif, number=10**5))
print(timeit.timeit(jan, number=10**5))
print(timeit.timeit(roadrunner, number=10**5))

产量

0.37175918000139063
0.49957343799906084
0.2700801329992828

Answer 3

a = [5, 2, 3, 1, 2, 3, 1, 3]
[a[i] for i in range(1,len(a)) if a[i] > a[i-1]]
# [5, 3, 2, 3, 3]

Answer 4

不使用zip 或每次按其索引访问元素的另一种解决方案

prev, *lst = [3, 5, 2, 3, 1, 2, 3, 1, 3]
greater = []
for i in lst:
    if prev < i:
        greater.append(i)
    prev = i

@Jan 提供的测试用例：

def mushif(lst):
    greater = []
    for i in range(1, len(lst)):
        if lst[i] > lst[i-1]:
            greater.append(lst[i])

def jan(lst):
    greater = [item[1] for item in filter(lambda x: x[1] > x[0], zip(lst, lst[1:]))]


def roadrunner(lst):
    greater =   [y for x, y in zip(lst, lst[1:]) if y > x]

def vishes_shell(lst):
    start, *lst = lst
    greater = []
    for i in lst:
        if start < i:
            greater.append(i)
        start = i

import timeit, functools, random
lst = [3, 5, 2, 3, 1, 2, 3, 1, 3]
print('Runnig with {} elements'.format(lst))
print('mushif', timeit.timeit(functools.partial(mushif, lst), number=10**5))
print('jan', timeit.timeit(functools.partial(jan, lst), number=10**5))
print('roadrunner', timeit.timeit(functools.partial(roadrunner, lst), number=10**5))
print('vishes_shell', timeit.timeit(functools.partial(vishes_shell, lst), number=10**5))

lst = [random.randint(1, 100) for _ in range(100)]
print('Runnig with 100 elements')
print('mushif', timeit.timeit(functools.partial(mushif, lst), number=10**5))
print('jan', timeit.timeit(functools.partial(jan, lst), number=10**5))
print('roadrunner', timeit.timeit(functools.partial(roadrunner, lst), number=10**5))
print('vishes_shell', timeit.timeit(functools.partial(vishes_shell, lst), number=10**5))

lst = [random.randint(1, 100) for _ in range(1000)]
print('Runnig with 1000 elements')
print('mushif', timeit.timeit(functools.partial(mushif, lst), number=10**5))
print('jan', timeit.timeit(functools.partial(jan, lst), number=10**5))
print('roadrunner', timeit.timeit(functools.partial(roadrunner, lst), number=10**5))
print('vishes_shell', timeit.timeit(functools.partial(vishes_shell, lst), number=10**5))

输出：

Runnig with [3, 5, 2, 3, 1, 2, 3, 1, 3] elements
mushif 0.22174075798830017
jan 0.367339823016664
roadrunner 0.16411117801908404
vishes_shell 0.16474426098284312

Runnig with 100 elements
mushif 1.8483440639975015
jan 2.6946504779916722
roadrunner 0.8267438650073018
vishes_shell 1.1597095750039443

Runnig with 1000 elements
mushif 21.29723681899486
jan 26.859666333009955
roadrunner 8.274298987002112
vishes_shell 12.677083582995692

如您所见，roadrunner 是最好的。

Answer 5

from itertools import islice
greater = [y for x,y in zip(a,islice(a,1,None)) if x < y]