Python program to find largest number in a list

Given a list of numbers, the task is to write a Python program to find the largest number in given list. 

Examples:

Input : list1 = [10, 20, 4]
Output : 20

Input : list2 = [20, 10, 20, 4, 100]
Output : 100

Method 1: Sort the list in ascending order and print the last element in the list.

Python3

# Python program to find largest
# number in a list

# list of numbers
list1 = [10, 20, 4, 45, 99]

# sorting the list
list1.sort()

# printing the last element
print("Largest element is:", list1[-1])

Output

Largest element is: 99

Time Complexity: O(nlogn)
Auxiliary Space: O(1)

Method 2: Using max() method

Python3

# Python program to find largest
# number in a list

# List of numbers
list1 = [10, 20, 4, 45, 99]

# Printing the maximum element
print("Largest element is:", max(list1))

Output

Largest element is: 99

Time complexity : O(n)
Auxiliary Space : O(1)

Method 3: Find the max list element on inputs provided by user 

Python3

# Python program to find largest
# number in a list

# Creating an empty list
list1 = []

# asking number of elements to put in list
num = int(input("Enter number of elements in list: "))

# Iterating till num to append elements in list
for i in range(1, num + 1):
    ele = int(input("Enter elements: "))
    list1.append(ele)

# Printing maximum element
print("Largest element is:", max(list1))

Output:

Enter number of elements in list: 4
Enter elements: 12
Enter elements: 19
Enter elements: 1
Enter elements: 99
Largest element is: 99

Time complexity : O(n)
Auxiliary Space : O(1)

Method 4: Without using built-in functions in Python: 

Python3

# Python program to find largest
# number in a list


def myMax(list1):

    # Assume first number in list is largest
    # initially and assign it to variable "max"
    max = list1[0]
# Now traverse through the list and compare
    # each number with "max" value. Whichever is
    # largest assign that value to "max'.
    for x in list1:
        if x > max:
            max = x

    # after complete traversing the list
    # return the "max" value
    return max


# Driver code
list1 = [10, 20, 4, 45, 99]
print("Largest element is:", myMax(list1))

Output

Largest element is: 99

Time complexity : O(n)
Auxiliary Space : O(1)

Method 5: Use the max() and def functions to find the largest element in a given list. The max() function prints the largest element in the list.  

Python3

# Python code to find the largest number
# in a list
def maxelement(lst):

  # displaying largest element
    # one line solution
    print(max(lst))


# driver code
# input list
lst = [20, 10, 20, 4, 100]
# the above input can also be given as
# lst = list(map(int, input().split()))
# -> taking input from the user
maxelement(lst)

Output

100

Time complexity : O(n)
Auxiliary Space : O(1)

Method: Using the lambda function

Python3

# python code to print largest element in the list

lst = [20, 10, 20, 4, 100]
print(max(lst, key=lambda value: int(value)) )

Output

100

Time complexity : O(n)
Auxiliary Space: O(n), where n is the length of the list.

Method: Using reduce function

Python3

from functools import reduce
lst = [20, 10, 20, 4, 100]
largest_elem = reduce(max, lst)
print(largest_elem)

Output

100

Time Complexity: O(n)
Auxiliary Space: O(1)

Method: Using recursion

Python3

# Function to find the largest element in the list
def FindLargest(itr, ele, list1):

  # Base condition
    if itr == len(list1):
        print("Largest element in the list is: ", ele)
        return

      # Check max condition
    if ele < list1[itr]:
        ele = list1[itr]

        # Recursive solution
    FindLargest(itr+1, ele, list1)

    return

  # input list
list1 = [2, 1, 7, 9, 5, 4]

FindLargest(0, list1[0], list1)

Output

Largest element in the list is:  9

Time Complexity: O(n)
Auxiliary Space: O(n)

Method: Using heapq.nlargest()

Here’s how you can use heapq.nlargest() function to find the largest number in a list:

Algorithm:

1. Import the heapq module.
2. Create a list of numbers.
3. Use the heapq.nlargest() function to find the largest element. The nlargest() function takes two arguments – the first argument is the number of largest elements to be returned, and the second argument is the list of numbers.
4. Retrieve the largest element from the list of largest elements returned by heapq.nlargest() function.
5. Print the largest element.

Python3

import heapq

# list of numbers
list1 = [10, 20, 4, 45, 99]

# finding the largest element using heapq.nlargest()
largest_element = heapq.nlargest(1, list1)[0]

# printing the largest element
print("Largest element is:", largest_element)

Output

Largest element is: 99

Time complexity: O(nlogk), where n is the length of the list and k is the number of largest elements to be returned. In this case, k is 1, so the time complexity is O(nlog1) = O(n).
Auxiliary Space: O(k), where k is the number of largest elements to be returned. In this case, k is 1, so the auxiliary space is O(1).

Method: Using np.max() method: 

Approach:

1. Initialize the test list. 
2. Use np.array() method to convert the list to numpy array. 
3. Use np.max() method on numpy array which gives the max element in the list. 

Python3

import numpy as np

# given list
list1 = [2, 7, 5, 64, 14]

# converting list to numpy array
arr = np.array(list1)

# finding largest numbers using np.max() method
num = arr.max()

# printing largest number
print(num)

Output:

64

Time Complexity: O(n) where n is the length of the list. 
Auxiliary Space: O(n) where n is the length of the list. because numpy array of length n is created.