Python program to find second largest number in a list

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

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

Input: list2 = [70, 11, 20, 4, 100]
Output: 70

Method 1: Sorting is an easier but less optimal method. Given below is an O(n) algorithm to do the same. 

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# Python program to find second largest
# number in a list
 
# list of numbers - length of
# list should be at least 2
list1 = [10, 20, 4, 45, 99]
 
mx=max(list1[0],list1[1])
secondmax=min(list1[0],list1[1])
n =len(list1)
for i in range(2,n):
    if list1[i]>mx:
        secondmax=mx
        mx=list1[i]
    elif list1[i]>secondmax and \
        mx != list1[i]:
        secondmax=list1[i]
 
print("Second highest number is : ",\
      str(secondmax))

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Output

Second highest number is :  45

Method 2: Sort the list in ascending order and print the second last element in the list. 

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# 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 second last element
print("Second largest element is:", list1[-2])

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Output



Second largest element is: 45

Method 3: By removing the max element from the list 

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# Python program to find second largest
# number in a list
 
# list of numbers
list1 = [10, 20, 4, 45, 99]
 
# new_list is a set of list1
new_list = set(list1)
 
# removing the largest element from temp list
new_list.remove(max(new_list))
 
# elements in original list are not changed
# print(list1)
 
print(max(new_list))

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Output

45

Method 4: Find max list element on inputs provided by the user 
 

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# Python program to find second largest
# number in a list
 
# creating 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)
 
'''
# sort the list   
list1.sort()
     
# print second maximum element
print("Second largest element is:", list1[-2])
 
'''
 
# print second maximum element using sorted() method
print("Second largest element is:", sorted(list1)[-2])

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Output: 

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



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