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Leetcode with dani
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Forwarded from Codeforces Official
Codeforces Round 1006 (Div. 3) will take place on the 25th of February at 14:35 UTC. 
Please, join by the link https://codeforces.com/contests/2072?locale=en
LeetCode Problem 525: Contiguous Array

Difficulty: Medium
Topics: Array, Hashing, Prefix Sum
Companies: Many top tech companies have featured similar problems in interviews
Link: Contiguous Array on LeetCode

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Problem Statement

Given a binary array nums, return the maximum length of a contiguous subarray with an equal number of 0 and 1.

A contiguous subarray is one where the elements are consecutive, and an equal number of 0s and 1s means that the sum (after a transformation) is 0.

Note:

• You can transform the array by replacing each 0 with -1.

• Then, the problem reduces to finding the largest subarray whose sum is 0.

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Examples

Example 1:
Input: nums = [0, 1]
Output: 2
Explanation: The entire array [0, 1] has one 0 and one 1.

Example 2:
Input: nums = [0, 1, 0]
Output: 2
Explanation: Either subarray [0, 1] or [1, 0] has an equal number of 0s and 1s.

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Approach Explanation

1. Transform the Array:
Replace every 0 with -1. This way, a subarray with an equal number of 0s and 1s will have a total sum of 0.

2. Prefix Sum Hash Map:

Prefix Sum: Compute the cumulative sum while iterating through the transformed array.

Hash Map: Use a dictionary to store the first occurrence of each cumulative sum.

Finding a Subarray: If the same cumulative sum is seen again, the subarray between these two indices has a sum of 0 (equal number of 0s and 1s).

Update Maximum Length: Calculate the length of the subarray and update the maximum length if this subarray is longer.

3. Efficiency:
This approach works in O(n) time and O(n) space, making it efficient for large inputs.

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Solution

def findMaxLength(nums):
# Replace 0 with -1 for transformation
for i in range(len(nums)):
if nums[i] == 0:
nums[i] = -1

cumulative_sum = 0
max_length = 0
sum_index_map = {} # To store the first occurrence of each cumulative sum

for i, num in enumerate(nums):
cumulative_sum += num

# Check if cumulative_sum is 0, which means subarray from index 0 to i is valid
if cumulative_sum == 0:
max_length = i + 1

# If cumulative_sum has been seen before, update max_length accordingly
if cumulative_sum in sum_index_map:
max_length = max(max_length, i - sum_index_map[cumulative_sum])
else:
sum_index_map[cumulative_sum] = i

return max_length

# Testing the function with provided examples
print(findMaxLength([0, 1])) # Output: 2
print(findMaxLength([0, 1, 0])) # Output: 2

▎Final Recap

This solution transforms the binary array into one that uses -1 instead of 0, so that we can use the cumulative sum to detect subarrays with equal numbers of 0s and 1s. By maintaining a hash map of the first occurrence of each cumulative sum, we can efficiently calculate the maximum length of any subarray with a sum of 0. This is a neat and efficient way to tackle the problem!

For more details, visit the problem link: Contiguous Array on LeetCode.
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Leetcode with dani
▎LeetCode Problem 525: Contiguous Array Difficulty: Medium Topics: Array, Hashing, Prefix Sum Companies: Many top tech companies have featured similar problems in interviews Link: Contiguous Array on LeetCode --- ▎Problem Statement Given a binary…
class Solution:
def findMaxLength(self, nums: List[int]) -> int:
s = {0:-1}
t = 0
maxm = 0
c1 = 0
c0 = 0
for i in range(len(nums)):
if nums[i]:
c1+=1
else:
c0+=1
if c1-c0 not in s:
s[c1-c0] = i
else:
maxm = max(maxm,i-s[c1-c0])
return maxm
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Leetcode with dani
https://leetcode.com/problems/remove-linked-list-elements/ Easy question for beginner to linked list
class Solution:
def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
dummy = ListNode(0,head)
p1 = dummy
p2 = dummy.next
while p2:
if p2.val==val:
p1.next = p2.next
p2 = p2.next
else:
p1 = p1.next
p2 = p2.next
return dummy.next
Leetcode with dani
https://leetcode.com/problems/remove-nth-node-from-end-of-list/
class Solution:
def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
dummy = ListNode(-1,head)
p1 = dummy
p2 = dummy.next
count = 0
while p2:
if count <n:
p2 = p2.next
count+=1
else:
p1 = p1.next
p2 = p2.next
if p1:
p1.next = p1.next.next
return dummy.next
Leetcode with dani
https://leetcode.com/problems/middle-of-the-linked-list/denoscription/
class Solution:
def middleNode(self, head: Optional[ListNode]) -> Optional[ListNode]:
p1 = head
p2 = head
while p2 and p2.next:
p1=p1.next
p2 = p2.next.next
return p1
Did you understand Floyd’s Cycle-Finding Algorithm for Linked List? It’s pretty cool and clever!
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Top 10 Non-Technical Interview Questions for FAANG Companies: Insights and Preparation Tips

🧠 Behavioral Leadership

1. "Tell me about a time you failed and what you learned."
Tests self-awareness and growth mindset.

2. "Describe a team conflict you resolved."
Assesses emotional intelligence and mediation skills.

3. "Share an example of showing leadership without authority."
Evaluates initiative and influence.

🎯 Career Motivation

4. "Why do you want to work here specifically?"
Probes company research and cultural fit.

5. "Where do you see yourself in 3-5 years?"
Checks alignment with company growth paths.

🌟 Strengths Values

6. "What unique value would you bring to this team?"
Reveals self-assessment accuracy.

7. "Describe your most innovative professional contribution."
Assesses creativity and business impact.

🛠 Work Approach

8. "How do you prioritize when facing multiple deadlines?"
Tests organizational and decision-making skills.

9. "Tell me about a project requiring deep analysis."
Examines problem-solving methodology.

🤝 Cultural Fit

10. "What does ideal team collaboration look like to you?"
Matches working style with company culture.

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▎Key Preparation Tips:

• Use the STAR (Situation-Task-Action-Result) format for behavioral answers.

• Align responses with FAANG leadership principles.

• Practice concise storytelling (90-120 seconds per answer).

• Research specific company values (e.g., Amazon's 16 Leadership Principles).

For 53 additional common questions and answer frameworks, refer to:
FAANG Behavioral Guide (https://igotanoffer.com/blogs/tech/faang-interview-questions)
Non-Technical Question Strategies (https://www.indeed.com/career-advice/interviewing/non-tech-interview-questions)
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What is the object-oriented method to get rich? Inherit it! 😂😂
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Problem: 2602. Minimum Operations to Make All Array Elements Equal

Difficulty: Medium
Topics: Array, Sorting, Binary Search, Prefix Sum


Problem Denoscription

You are given an array nums consisting of positive integers. You are also given an integer array queries of size m. For the ith query, you want to make all the elements of nums equal to queries[i]. You can perform the following operation on the array any number of times:

Operation: Increase or decrease an element of the array by 1.

Return an array answer of size m where answer[i] is the minimum number of operations required to make all elements of nums equal to queries[i].

Note: After each query, the array is reset to its original state.

Examples

Example 1:

Input:
nums = [3, 1, 6, 8]
queries = [1, 5]



Output:

[14, 10]



Explanation:

• For the first query (q = 1):

• Decrease nums[0] 2 times: from 3 to 1.

• Decrease nums[2] 5 times: from 6 to 1.

• Decrease nums[3] 7 times: from 8 to 1.

• Total operations = 2 + 5 + 7 = 14.

• For the second query (q = 5):

• Increase nums[0] 2 times: from 3 to 5.

• Increase nums[1] 4 times: from 1 to 5.

• Decrease nums[2] 1 time: from 6 to 5.

• Decrease nums[3] 3 times: from 8 to 5.

• Total operations = 2 + 4 + 1 + 3 = 10.

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Example 2:

Input:

nums = [2, 9, 6, 3]
queries = [10]



Output:

[20]



Explanation:

• Increase each element in the array to 10:

• Operations for each element:

• 8 (from 2 to 10),

• 1 (from 9 to 10),

• 4 (from 6 to 10),

• 7 (from 3 to 10).

• Total operations = 8 + 1 + 4 + 7 = 20.

▎Constraints

• n = nums.length

• m = queries.length

• 1 ≤ n, m ≤ 10⁵

• 1 ≤ nums[i], queries[i] ≤ 10⁹

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