Next Greater Element Using Stack in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push the current element onto the stack.

DSA Python

stack.[1](arr[i])

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Apop

Bappend

Cpush

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append.

Using push which is not a Python list method.

In Python, to add an element to the end of a list (used as a stack), we use append().

2fill in blank

medium

Complete the code to pop the top element from the stack.

DSA Python

top = stack.[1]()

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Apop

Bremove

Cdelete

Ddiscard

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove which removes by value, not by position.

Using delete which is not a list method.

pop() removes and returns the last element from the list, which is the top of the stack.

3fill in blank

hard

Fix the error in the while loop condition to check if stack is not empty.

DSA Python

while stack and stack[-1] [1] arr[i]:

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A<

B>

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using greater than or equal operators which reverse the logic.

Using less than or equal which includes equal values incorrectly.

We want to pop elements smaller than the current element, so the condition is stack[-1] < arr[i].

4fill in blank

hard

Fill both blanks to complete the dictionary comprehension for the next greater element.

DSA Python

result = {num: [1] for num in arr if num [2] -1}

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Astack[-1]

B==

C!=

Darr[-1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which would only include the last element.

Using arr[-1] which is the last element of the array, not the next greater element.

We map each number to the top of the stack (next greater element), excluding the last element which has no next greater element.

5fill in blank

hard

Fill all three blanks to complete the function that finds the next greater element for each item in the list.

DSA Python

def next_greater_element(arr):
    stack = []
    result = {}
    for i in range([1]):
        while stack and stack[-1] < arr[i]:
            result[stack.pop()] = arr[i]
        stack.[2](arr[i])
    for num in stack:
        result[num] = [3]
    return result

Drag options to blanks, or click blank then click option'

Alen(arr)

Bappend

C-1

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect loop range.

Using push instead of append.

Assigning -1 instead of None for no next greater element.

We loop through the entire array length, append elements to the stack, and assign None to elements with no next greater element.