Insert an item into sorted list in Python

Question

I'm creating a class where one of the methods inserts a new item into the sorted list. The item is inserted in the corrected (sorted) position in the sorted list. I'm not allowed to use any built-in list functions or methods other than [], [:], +, and len though. This is the part that's really confusing to me.

What would be the best way in going about this?

Answer 1

Use the insort function of the bisect module:

import bisect 
a = [1, 2, 4, 5] 
bisect.insort(a, 3) 
print(a)

Output

[1, 2, 3, 4, 5] 

Answer 2

Hint 1: You might want to study the Python code in the bisect module.

Hint 2: Slicing can be used for list insertion:

>>> s = ['a', 'b', 'd', 'e']
>>> s[2:2] = ['c']
>>> s
['a', 'b', 'c', 'd', 'e']

Answer 3

You should use the bisect module. Also, the list needs to be sorted before using bisect.insort_left

It's a pretty big difference.

>>> l = [0, 2, 4, 5, 9]
>>> bisect.insort_left(l,8)
>>> l
[0, 2, 4, 5, 8, 9]

timeit.timeit("l.append(8); l = sorted(l)",setup="l = [4,2,0,9,5]; import bisect; l = sorted(l)",number=10000)
    1.2235019207000732

timeit.timeit("bisect.insort_left(l,8)",setup="l = [4,2,0,9,5]; import bisect; l=sorted(l)",number=10000)
    0.041441917419433594

Answer 4

I'm learning Algorithm right now, so i wonder how bisect module writes. Here is the code from bisect module about inserting an item into sorted list, which uses dichotomy:

def insort_right(a, x, lo=0, hi=None):
    """Insert item x in list a, and keep it sorted assuming a is sorted.
    If x is already in a, insert it to the right of the rightmost x.
    Optional args lo (default 0) and hi (default len(a)) bound the
    slice of a to be searched.
    """

    if lo < 0:
        raise ValueError('lo must be non-negative')
    if hi is None:
        hi = len(a)
    while lo < hi:
        mid = (lo+hi)//2
        if x < a[mid]:
            hi = mid
        else:
            lo = mid+1
    a.insert(lo, x)

Answer 5

This is a possible solution for you:

a = [15, 12, 10]
b = sorted(a)
print b # --> b = [10, 12, 15]
c = 13
for i in range(len(b)):
    if b[i] > c:
        break
d = b[:i] + [c] + b[i:]
print d # --> d = [10, 12, 13, 15]

Answer 6

# function to insert a number in an sorted list


def pstatement(value_returned):
    return print('new sorted list =', value_returned)


def insert(input, n):
    print('input list = ', input)
    print('number to insert = ', n)
    print('range to iterate is =', len(input))

    first = input[0]
    print('first element =', first)
    last = input[-1]
    print('last element =', last)

    if first > n:
        list = [n] + input[:]
        return pstatement(list)
    elif last < n:
        list = input[:] + [n]
        return pstatement(list)
    else:
        for i in range(len(input)):
            if input[i] > n:
                break
    list = input[:i] + [n] + input[i:]
    return pstatement(list)

# Input values
listq = [2, 4, 5]
n = 1

insert(listq, n)

Answer 7

Well there are many ways to do this, here is a simple naive program to do the same using inbuilt Python function sorted()

def sorted_inserter():
list_in = []
n1 = int(input("How many items in the list : "))

for i in range (n1):
    e1 = int(input("Enter numbers in list : "))
    list_in.append(e1)
print("The input list is : ",list_in)


print("Any more items to be inserted ?")
n2 = int(input("How many more numbers to be added ? : "))
for j in range (n2):
    e2= int(input("Add more numbers : "))
    list_in.append(e2)
    list_sorted=sorted(list_in)
    print("The sorted list is: ",list_sorted)
    

sorted_inserter()

The output is

How many items in the list : 4

Enter numbers in list : 1

Enter numbers in list : 2

Enter numbers in list : 123

Enter numbers in list : 523

The input list is : [1, 2, 123, 523]

Any more items to be inserted ?

How many more numbers to be added ? : 1

Add more numbers : 9

The sorted list is: [1, 2, 9, 123, 523]

Answer 8

This is the best way to append the list and insert values to sorted list:

 a = [] num = int(input('How many numbers: ')) for n in range(num):
     numbers = int(input('Enter values:'))
     a.append(numbers)

 b = sorted(a) print(b) c = int(input("enter value:")) for i in
 range(len(b)):
     if b[i] > c:
         index = i
         break d = b[:i] + [c] + b[i:] print(d)`