# Citadel

[longest\_non\_decreasing\_subarray](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dp/longest_non_decreasing_subarray "mention")

[number\_of\_good\_binary\_strings](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dp/number_of_good_binary_strings "mention")

[minimum\_knight\_moves](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/bfs/minimum_knight_moves "mention")

[delete\_and\_earn](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dp/delete_and_earn "mention")

[maximum\_path\_sum](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/binary_tree/maximum_path_sum "mention")

[lfu\_cache](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/design/lfu_cache "mention")

[lru\_cache](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/design/lru_cache "mention")

[knight\_probability\_in\_board](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/bfs/knight_probability_in_board "mention")

[robot\_room\_cleaner](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dfs/robot_room_cleaner "mention")

[minimum\_height\_tree](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/bfs/minimum_height_tree "mention")

[evaluate\_reverse\_polish\_notation](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/stack/evaluate_reverse_polish_notation "mention")

[get\_random](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/design/get_random "mention")

[validate\_bst](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/binary_search_tree/validate_bst "mention")

[find\_duplicate\_num](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/array/find_duplicate_num "mention")

[permutations](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/backtracking/permutations "mention")

[buy\_and\_sell\_stock](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dp/buy_and_sell_stock "mention")

[house\_robber](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dp/house_robber "mention")

[subarray\_sum\_k](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/prefix_sum/subarray_sum_k "mention")

[n\_queens](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/backtracking/n_queens "mention")

[range\_addition](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/prefix_sum/range_addition "mention")

[minimum\_costs\_using\_train\_line](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/dp/minimum_costs_using_train_line "mention")

[smallest\_range\_ii](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/greedy/smallest_range_ii "mention")

[fibonacci](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/company-tags/citadel/fibonacci "mention")

[pi](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/company-tags/citadel/pi "mention")

[probability](https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/company-tags/citadel/probability "mention")

## Python

```python
nums = [1,2,3]
nums.append(1)
nums.pop()
nums.sort()

# Dictionary
dict = {'a':1,'b':2,'c':3}
dict.keys() # returns list of keys of dictionary
dict.values() # returns list of values of dictionary

dict.get('a') # returns value for any corresponding key
dict.items() # returns [('a',1),('b',2),('c',3)]
dict.pop(KEY) # pops key-value pair with that key

# A double-ended queue, or deque, has the feature of adding and removing elements from either end.
from collections import deque

queue = deque(['name','age','DOB'])

queue.append("append_from_right") # Append from right
queue.pop() # Pop from right

queue.appendleft("fromLeft") # Append from left
queue.popleft() # Pop from left

# min heap
nums = [5, 7, 9, 1, 3]
heapq.heapify(nums) # converts list into heap. Can be converted back to list by list(nums).
heapq.heappush(nums,element) # Push an element into the heap
heapq.heappop(nums)

# max heap
nums = [5, 7, 9, 1, 3]
nums = [-num for num in nums]  # Negate all elements
heapq.heapify(nums)  #
largest_element = -heapq.heappop(nums)


text = 'Python is a fun programming language'

# split the text from space
print(text.split(' '))
name = "M3onica Gell22er "
print(name.isalnum()) # Output : False
#The isalpha() method returns True if all characters in the string are alphabets. If not, it returns False
name = "Monica"
print(name.isalpha()) #output true

```


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