Return index of maximum number in a list using enumerate

Question

I have a list a = [5, 1, 2, 3, 4, 5] My program should return a list of the "indexes" of the maximum value, in this case [0, 5] but I'm using enumerate and not the actual index.

a = [5, 1, 2, 3, 4, 5]
a2 = enumerate(a)
result = list(a2)
print(result)

This now gives me [(0, 5), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5)] but I'm unsure of how to return 0 and 5 from here. I can find them individually by trying

print(result[0][0])
print(result[5][0])

but having trouble iterating over the list of tuples to find the first element where the second element is the maximum value. I'm thinking I need to use the max function but again unsure of the syntax this should take.

sahasrara62 · Answer 1 · 2021-12-06T12:16:13.340

1

JUst get the max value of a list using max function. and then using enumerator match the max value with the value if the list . if they matched then store the index

max_value = max(a)
result = [index for index, value in enumerate(a) if value==max_value]

if dont want to use max function, and done the task in O(n) then

a = [5, 1, 2, 3, 4, 5,1,1,1,4,999999]

save_index = {}
largest = -99999999999 

for i, v in enumerate(a):
    if v>largest:
        largest=v
    if v not in save_index:
        save_index[v]=[i]
    else:
        save_index[v].append(i)

result = save_index[largest]
print(result)
# output 10

edited Dec 06 '21 at 12:16

answered Dec 06 '21 at 12:05

sahasrara62

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The first code is also O(n)... – Tomerikoo Dec 06 '21 at 12:21
@Tomerikoo yes, but just used `max` there, second one is without it – sahasrara62 Dec 06 '21 at 12:22
Still, `max` simply iterates the list which is O(n)... – Tomerikoo Dec 06 '21 at 12:22
yeah, both are O(n), difference is the memory usage and in first one we have to traverse through list 2 times (one while calulating max, and second to calcluate index), in second on it is just 1 time traversal with more memory usage – sahasrara62 Dec 06 '21 at 12:24
By the way you can use a `defalutdict` to simplify the second code – Tomerikoo Dec 06 '21 at 12:25
yes, but doesn't want to use any other function other than `enumerator` – sahasrara62 Dec 06 '21 at 12:26
1

It's called `enumerate` and nowhere it says you're not allowed to use anything. The OP just said that they are trying to use `enumerate`... – Tomerikoo Dec 06 '21 at 12:27
yes, it can be solved in other ways also, just want to stick with basic code using DS and without using any library – sahasrara62 Dec 06 '21 at 12:29

score 1 · Answer 2 · edited Dec 06 '21 at 12:21

1

If you're allowed to use max it's very easy:

a = [5, 1, 2, 3, 4, 5]
results = [index for index, value in enumerate(a) if value == max(a)]

This is very inefficient as it runs max(a) on every iteration. Plus if you're unable to use max at all (because this sounds like an assignment) or if efficiency matters, you could do max first before the loop

results are [0, 5]

edited Dec 06 '21 at 12:21

Tomerikoo

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answered Dec 06 '21 at 12:07

Ofer Sadan

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score 0 · Answer 3 · answered Dec 06 '21 at 12:04

0

The good thing about lists is that you can use function max() and pass the list as a parameter to it. You can also use list comprehension to build your resulting output.

res = [i  for i in range(len(a)) if a[i]==max(a)]

answered Dec 06 '21 at 12:04

Fatemeh Sangin

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Return index of maximum number in a list using enumerate

3 Answers3