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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: "amanaplanacanalpana
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 open bracket of the sa
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: [5,6,7,1,2,3,4] Explanat
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.
Explains what makes a problem a DP candidate, showing both memoization and tabulation solving the same example.
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