Neetcode-150

Problem Statement We have to implement the reorderList function that takes the head node of a linked list as input and reorders its nodes in the format specified below. Given an input list like the following: $$Node_0 \rightarrow Node_1 \rightarrow Node_2 \rightarrow \dots \rightarrow Node_{(n-2)} \rightarrow Node_{(n-1)} \rightarrow Node_n$$ the reorderList function should reorder its nodes as: $$Node_0 \rightarrow Node_n \rightarrow Node_1 \rightarrow Node_{(n-1)} \rightarrow Node_2 \rightarrow Node_{(n-2)} \rightarrow \dots$$ ...

Problem Statement We have to implement the mergeTwoLists function that takes the head nodes of two sorted linked lists as input and returns the head node of the merged linked list as the output. Optimal Solution To merge both linked lists we can use the two-pointer approach by maintaining an iterator on both linked lists and comparing their values. The smaller value will be selected and inserted at the end of a new list. The result would be a merged sorted linked list. ...

Problem Statement We have to implement the reverseList function that takes the head node of a linked list as an input and returns the head node of the reversed linked list in the output. Brute Force Solution If we iterate over the input linked list and insert its value at the beginning of a new list the result would be a reversed linked list. ...

Problem Statement We have to implement the longestConsecutive function that takes an integer array as input and returns the length of the longest sequence of consecutive integers. For example, in array [4, 2, 7, 8, 1, 5, 6, 0] we have two sequences of consecutive integers: [0, 1, 2] and [4, 5, 6, 7, 8]. The longest sequence ([4, 5, 6, 7, 8]) has length 5. ...

Problem Statement We have to implement an encode function that takes a list of string values as input and returns a single encoded string that could be transmitted over a network. On the other side of the network, the decode function will take the encoded string as input and return the original list of string values as output. A delimiter could be used to differentiate between words. For example, ["Hello", "World"] could be encoded with comma delimiter (,) to "Hello,World". ...

Problem Statement We have to implement an isValidSudoku function that takes a 9x9 matrix (representing a Sudoku grid) as input and returns true if the grid is valid and false otherwise. Sudoku Grid A Sudoku grid is valid if Every row contains digits from 1 to 9 without repetition. Rows in a Sudoku Grid Every column contains digits from 1 to 9 without repetition. ...

Problem Statement We have to implement a productExceptSelf function that takes an integer array nums as input and returns another array answer as output. The element answer[i] will be the product of all elements in inputArray except inputArray[i]. The implementation should not contain a division (/) operation because the answer array could also be created by iterating over all elements in inputArray and dividing them from the product of the complete array. ...

Problem Statement We have to implement a topKFrequent function that takes an integer array and a value k as input and returns the k most frequent elements in the input array. For example, topKFrequent({1, 1, 2, 2, 3, 5, 2}, 2) will return the top 2 most frequent elements in the array i.e. {2, 1}. If multiple elements have the same frequency, then any of them could be returned in the solution as long as its length is k. ...

Problem Statement We have to implement a groupAnagram function that takes an array of strings as input and returns a new array with anagrams grouped. The input string array is assumed to be composed entirely of lowercase English characters. Brute Force Solution If two strings are anagrams then their sorted order will be the same. Thus, anagrams could be grouped under their sorted order. ...

Problem Statement We have to implement a twoSums() function that takes an integer array and a target value as inputs. It returns the indexes of two elements in the input array which could be summed up to the target value. It is assumed that the input array contains only one valid pair of elements that sum up to the target value. Brute Force Solution The brute-force solution will find the sum of all element pairs in the array using nested loops. ...