Monthly Archives: October 2022

C# || How To Return The Top K Frequent Words In Array Of Strings Using C#

The following is a module with functions which demonstrates how to get the top K frequent words in an array of strings using C#.


1. Top K Frequent – Problem Statement

Given an array of strings words and an integer k, return the k most frequent strings.

Return the answer sorted by the frequency from highest to lowest. Sort the words with the same frequency by their lexicographical order.

Example 1:


Input: words = ["i","love","leetcode","i","love","coding"], k = 2
Output: ["i","love"]
Explanation: "i" and "love" are the two most frequent words.
Note that "i" comes before "love" due to a lower alphabetical order.

Example 2:


Input: words = ["the","day","is","sunny","the","the","the","sunny","is","is"], k = 4
Output: ["the","is","sunny","day"]
Explanation: "the", "is", "sunny" and "day" are the four most frequent words, with the number of occurrence being 4, 3, 2 and 1 respectively.


2. Top K Frequent – Solution

The following are two solutions which demonstrates how to get the top K frequent words in an array of strings.

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output for the example cases:


["i","love"]
["the","is","sunny","day"]

C# || Two Sum IV – How To Get Two Numbers In Binary Search Tree Equal To Target Value Using C#

The following is a module with functions which demonstrates how to get two numbers in a binary search tree equal to target value using C#.


1. Find Target – Problem Statement

Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.

Example 1:

Example 1


Input: root = [5,3,6,2,4,null,7], k = 9
Output: true

Example 2:

Example 2


Input: root = [5,3,6,2,4,null,7], k = 28
Output: false


2. Find Target – Solution

The following are two solutions which demonstrates how to get two numbers in a binary search tree equal to target value.

Both solutions use a set to keep track of the items already seen.

Each time a new node is encountered, we subtract the target value from the current node value. If the difference amount from subtracting the two numbers exists in the set, a 2 sum combination exists in the tree

1. Recursive

The following solution uses Depth First Search when looking for the target value.

2. Iterative

The following solution uses Breadth First Search when looking for the target value.

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output for the example cases:


true
false

C# || Counting Bits – How To Return The Number Of 1’s In Binary Representation Of X Using C#

The following is a module with functions which demonstrates how to return the number of 1’s in binary representation of X using C#.


1. Count Bits – Problem Statement

Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1‘s in the binary representation of i.

Example 1:


Input: n = 2
Output: [0,1,1]
Explanation:
0 --> 0
1 --> 1
2 --> 10

Example 2:


Input: n = 5
Output: [0,1,1,2,1,2]
Explanation:
0 --> 0
1 --> 1
2 --> 10
3 --> 11
4 --> 100
5 --> 101


2. Count Bits – Solution

The following is a solution which demonstrates how return the number of 1’s in binary representation of X.

In this problem, we can see a pattern start to form.

When the current n is even, we can get the answer by dividing by 2 (e.g result[n] = result[n / 2])

When the current n is odd, we can get the answer by getting the result at previous index and adding 1 (e.g result[n] = result[n – 1] + 1)

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output for the example cases:


[0,1,1]
[0,1,1,2,1,2]