Python – Maximum element till K value

One of the problem that is basically a subproblem for many complex problems, finding maximum number till a certain number in list in python, is commonly encountered and this particular article discusses possible solutions to this particular problem. Method #1 : Naive method The most common way this problem can be solved is using a loop and just max the occurrences of elements that are till given number K. 

Python3

# Python 3 code to demonstrate
# Maximum element till K value
# using naive method

# initializing list
test_list = [1, 7, 5, 6, 3, 8]

# initializing k
k = 4

# printing list
print ("The list : " + str(test_list))

# using naive method
# Maximum element till K value
res = 0
for i in test_list :
    if i <= k :
        res = max(res, i)

# printing the intersection
print ("The maximum number till K : " + str(res))

Output : 

The list : [1, 7, 5, 6, 3, 8]
The maximum number till K : 3

Time complexity: O(n), where n is the length of the test_list. 
Auxiliary Space: O(1), constant extra space is required

Method #2 : Using list comprehension This method achieves this task in a similar way, but in a more concise manner. List comprehension always lowers the lines of codes in the program even though runs a similar approach in the background. 

Python3

# Python 3 code to demonstrate
# Maximum element till K value
# using list comprehension

# initializing list
test_list = [1, 7, 5, 6, 3, 8]

# initializing k
k = 4

# printing list
print ("The list : " + str(test_list))

# using list comprehension
# Maximum element till K value
res = max([i for i in test_list if i <= k])

# printing the intersection
print ("The maximum number till K : " + str(res))

Output : 

The list : [1, 7, 5, 6, 3, 8]
The maximum number till K : 3

Time complexity: O(n), where n is the length of the test_list. 
Auxiliary Space: O(1), constant extra space is required

 Method #3 : Using sorted()

Approach

Sort the list in descending order and then take the Kth element from the sorted list.

Step-by-step algorithm

1. Define a function called max_element_till_k that takes two arguments: a list and an integer K.
2. Slice the list to get the first K elements, and store it in a variable called sliced_list.
3. Sort the sliced_list in descending order using the sorted() function with the reverse=True argument, and store it in a variable called sorted_list.
4. Return the first element of the sorted_list using index notation, which will be the maximum element in the list till the K value.

Python3

def max_element_till_k(lst, k):#define list and k
    sorted_list = sorted(lst[:k], reverse=True)#sort the list upto k value
    return sorted_list[0]# get the maximum element in sorted list
lst = [3, 5, 2, 8, 1, 9, 4]#input
k = 5#k value
max_val = max_element_till_k(lst, k)#max value
print(max_val) #print output

Output

8

Time complexity: O(klogk), where k is the upper limit of the range in which the maximum number has to be found

Space complexity: O(k), where k is the upper limit of the range in which the maximum number has to be found