LeetCode's Top 10 Most Popular Algorithm Questions and How to Solve Them

LeetCode is a popular platform for preparing for technical interviews and honing your algorithm skills. With over 1700 algorithm questions, it can be overwhelming to know where to start. That's why we've compiled a list of LeetCode's top 10 most popular algorithm questions and how to solve them.

Two Sum: Given an array of integers, return the indices of the two numbers such that they add up to a specific target.
To solve this problem, we can use a hash table to store the elements of the array and their indices. For each element in the array, we check if the target minus the current element is in the hash table. If it is, we have found our two elements. Otherwise, we add the current element and its index to the hash table.

Reverse Integer: Given a 32-bit signed integer, reverse digits of an integer.
To solve this problem, we can convert the integer to a string, reverse the string, and then convert it back to an integer. We also need to check for overflow and return 0 if the reversed integer is out of the range of a 32-bit signed integer.

Palindrome Number: Determine whether an integer is a palindrome.
To solve this problem, we can convert the integer to a string and then check if the string is the same forwards and backwards. We can also solve this problem without converting the integer to a string by comparing the first and last digits, second and second-to-last digits, and so on.

Longest Common Prefix: Write a function to find the longest common prefix string amongst an array of strings.
To solve this problem, we can sort the array of strings and then compare the first and last strings to find the common prefix. We can also use a trie (prefix tree) to find the longest common prefix in linear time.

Remove Duplicates from Sorted Array: Given a sorted array, remove the duplicates in-place such that each element appears only once and return the new length.
To solve this problem, we can use two pointers: one to iterate through the array and another to keep track of the next unique element. When we find a duplicate, we skip it and continue iterating.

Best Time to Buy and Sell Stock: Say you have an array for which the ith element is the price of a given stock on day i. If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.
To solve this problem, we can keep track of the minimum price seen so far and the maximum profit that can be made. We can then iterate through the array and update the minimum price and maximum profit as we go.

Merge Two Sorted Lists: Merge two sorted linked lists and return it as a new list.
To solve this problem, we can create a new dummy node and then compare the first elements of each list. We add the smaller element to the dummy node and move its pointer forward, and then repeat this process until one list is empty.

Valid Parentheses: Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
To solve this problem, we can use a stack to keep track of the opening parentheses. For each character in the string, we check if it is an opening parenthesis, if it is we push it to the stack, if it is a closing parenthesis we check if it matches the