Get the last negative element index from list-CodePudding

I'm struggling with this one, using basic codes to get the last index of the negative element (I'm not sure how to describe this but i will leave the problem down here)

n=[1,5,-3,7,3,-1,9] => This is supposed to be random number but i will leave this list as an example
Output : n=[-2]

Please help, Thanks in advance

CodePudding user response：

for i, element in enumerate(n):
    if element < 0:
        last_negative_index = i

from_end = last_negative_index - len(n)

CodePudding user response：

Here is a way to find the index of the last negative element of a list:

idx = next((len(n)-j-1 for j in range(len(n)) if n[len(n)-j-1] < 0), None)

This approach has optimal complexity (you look at every single element of the list only once).

An alternative:

idx = next((j for j in reversed(range(len(n))) if n[j] < 0), None)

CodePudding user response：

I hope this will work.

n = [1, 5, -3, 7, 3, -1, 9]

p = [-1, 5, 3, 7, 3, 1, 9]

print(max([n.index(x) for x in n if x<0]))

print(max([n.index(y) for y in p if y<0]))

OUTPUT

If you would like to have the output as the negative indexes of the list, you may use the expression below. However, this will give all outputs as negative indexes.

n = [1, 5, -3, 7, 3, -1, 9]

print(max([n.index(x)-len(n) for x in n if x<0]))

OUTPUT

-2

CodePudding user response：

You can search with starting from the last element this will give you the last index if the negative element exists

index = len(L)
while(index>=0):
   index-=1
   if L[index]<0 :
      break
print(index-len(L))