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Given a string s, find the first nonrepeating character in it and return its index. If it does not exist, return 1. Constraints: s consists of only lowercase English letters. 1 <= s.length <= 10^5 Examples: Input: s = "leetcode" Output: 0 Input: s = "loveleetcode" Output: 2 Input…
Given a nonempty array of integers nums, every element appears twice except for one. Find that single one. Constraints: The array nums is nonempty. Each element in the array appears twice, except for one element which appears only once. Example: Input: nums = [2,2,1] Output: 1 An…
You are given the heads of two sorted linked lists, list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Constraints: The number of nodes in both lists…
You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in lefttoright order. The large integer does not contain any leading zeros, except for the…
Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique, and you may return the result in any order. Constraints: 1 <= nums1.length, nums2.length <= 1000 0 <= nums1[i], nums2[i] <= 1000 Example: Input: nums1 = [1,…
Given a sorted array nums, remove the duplicates inplace such that each unique element appears only once. The relative order of the elements should be kept the same. Your function should return the new length k after removing the duplicates. Do not allocate extra space for anothe…
Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "". All given inputs are lowercase English letters az. The number of strings n will be between 0 and 200. The length of each string will be…
Given an array of strings strs, group the anagrams together. You can return the answer in any order. An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. Constraints: 1 <= strs.lengt…
You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from thi…
Given an integer array nums, determine if it contains any duplicates. Return true if any value appears at least twice in the array, and return false if every element is distinct. Constraints: 1 <= nums.length <= 10^5 10^9 <= nums[i] <= 10^9 Example: Input: nums = [1,2,3,1] Output…
Given an input string s, reverse the order of the words. Constraints: A word is defined as a sequence of nonspace characters. Words are separated by at least one space. The input string may contain leading or trailing spaces. Multiple spaces between two words should be reduced to…
You are given an array nums containing n distinct numbers in the range [0, n]. Your task is to find and return the only number in the range that is missing from the array. n is the length of nums. 1 <= n <= 10^4 0 <= nums[i] <= n All numbers in nums are unique. Example 1: Input:…
A palindrome is a sequence of characters that reads the same forwards and backwards. Given a string s, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example: Input: s = "A man, a plan, a canal: Panama" Output: true Explanation:…
Given a string s containing just the characters (, ), {, }, [, ], determine if the input string is valid. A string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding op…
Given an integer array nums, rotate the array to the right by k steps, where k is nonnegative. You must do this inplace with O(1) extra space. Constraints: 1 <= nums.length <= 10^5 2^31 <= nums[i] <= 2^31 1 0 <= k <= 10^5 Example: Input: nums = [1,2,3,4,5,6,7], k = 3 Output: [5,6…
Given a string s, find the first nonrepeating character in it and return its index. If it does not exist, return 1.The string s consists of only lowercase English letters.
A practical step-by-step framework for approaching any DSA interview question, from clarifying requirements to testing edge cases.
Explains the time-space tradeoff using memoization and hash tables as examples, with guidance on which resource to prioritize.
Explains greedy algorithms with a working coin-change example and a broken one, showing exactly when greedy fails.
Compares memoization and tabulation side by side, with clear guidance on which one to reach for and when.