Having problem in compiling this Greedy Algorithm's python question

Question

I was trying this question which is a greedy algorithm question. The celebration party problem. When i run it , as you can see below, it says list indices must be integer.. Can you help me with this, I am new to algorithm coding. I am also open to better and effective solutions.

Problem:

a=[1,5.4,2.1,3.4,3.1,2.0,1.8,8.9,10,23,4,5,5,2,1.6,1.9]
a.sort()
q=0
z={}
for i in range(len(a)):
    if (a[q]+1.0)>=a[i]:
        if q not in z.keys():
            z[q]=[]
        z[q].append(a[i])
    else:
        q=a[i]
        if q not in z.keys():
            z[q]=[]
        z[q].append(a[i])

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-32-60bee6e37157> in <module>
      4 z={}
      5 for i in range(len(a)):
----> 6     if (a[q]+1.0)>=a[i]:
      7         if q not in z.keys():
      8             z[q]=[]

TypeError: list indices must be integers or slices, not float

I am trying to, but I am not able to, i can not post image in question since I am new , and as of now I will have to wait for 90 minutes to add another question. — Rohit Rajsurya Prasad, Apr 05 '20 at 20:25
Do not add an image, add the code by editing the question. It will not be helpful to make a new question. — 001001, Apr 05 '20 at 20:26
You should edit the question, then copy the code and the error message. Next you select the part you added (the code text) and click on the {} symbol that says code block. — 001001, Apr 05 '20 at 20:29
Well the problem you had specifically is a trivial issue with existing answers so it wont help to change it. However, if my answer does not help you, you will need to post the expected output of the algorithm so people can help. — 001001, Apr 05 '20 at 20:43

score 0 · Answer 1 · answered Apr 05 '20 at 20:37

At the start of your else block, you say q=a[i]. As you have floats in a, at some point in your loop, q is being set to a float. Even if that float is something like 2.0, python will still raise an error when you try to use it as an index of a list. To solve this, you need to remove all floats from the list a.

score 0 · Accepted Answer · answered Apr 05 '20 at 20:38

The problem is with using q after you have assigned it to the values in a

a=[1,5.4,2.1,3.4,3.1,2.0,1.8,8.9,10,23,4,5,5,2,1.6,1.9]
a.sort()
q=0
z={}
for i in range(len(a)):
    if (a[q]+1.0)>=a[i]: # this is the problem that you have an error
        if q not in z.keys():
            z[q]=[]
        z[q].append(a[i])
    else:
        q=a[i] #here you are assigned the value to q, which can be a float
        if q not in z.keys():
            z[q]=[]
        z[q].append(a[i])

When you check if (a[q]+1.0)>=a[i], it is taking the list a and checking the index using the value q. Since that value can be a float, you can have the error, since index must be an int.

You can change the loop to track the index instead:

a=[1,5.4,2.1,3.4,3.1,2.0,1.8,8.9,10,23,4,5,5,2,1.6,1.9]
a.sort()
q=0
qidx=0
z={}
for i in range(len(a)):
    if (a[qidx]+1.0)>=a[i]:
        if q not in z.keys():
            z[q]=[]
        z[q].append(a[i])
    else:
        q=a[i]
        qidx = i
        if q not in z.keys():
            z[q]=[]
        z[q].append(a[i])

Which will output

{0: [1, 1.6, 1.8, 1.9, 2.0, 2], 2.1: [2.1, 3.1], 3.4: [3.4, 4], 5: [5, 5, 5.4], 8.9: [8.9], 10: [10], 23: [23]}

@RohitRajsuryaPrasad great, if you click the check to mark as accepted, others will know they don't need to also answer. — 001001, Apr 05 '20 at 20:46

Having problem in compiling this Greedy Algorithm's python question

2 Answers2