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Counting Palindromic Substrings This section addresses the problem of counting all palindromic substrings within a given string, similar to LeetCode problem 647. Problem Description Given a string s, determine and return the total count of palindromic substrings. A substring is a contiguous sequence of charcaters. A palindromic string reads the ...

Problem Description Given the head of a singly linked list, determine if the list is a palindrome. Return true if it is, otherwise return false. An optimal solution achieves O(n) time complexity and O(1) space complexity by combining a fast-slow pointer approach to find the middle node with a reversal of the latter half of the list. Algorithm O ...

Combination Sum The objective is to find all unique combinations from a list of candidate numbers that sum up to a given target. Each number may be used multiple times. The solution uses recursive backtracking with the following approach: Parameters include the candidate array, target value, current combination, and results collection Terminat ...

Online Judge Reference: http://ybt.ssoier.cn:8088/problem_show.php?pid=1974 Core Concepts The problem requires identifying dates that are both valid calendar dates and palindromes. A naive approach iterates through every 8-digit number between the start and end dates, resulting in a complexity of O(10^8). While this might pass, it is computat ...

Spinning Around Given a binary string (S) of length (n) with exactly one 1. In each operation, you can reverse a substring of length (k). For each position (i), find the minimum number of operations to move the 1 to position (i). Some positions are forbidden and cannot hold the 1 during the process. If no such number exists, output (-1). (n \le ...

Given a string s consisting exclusively of the characters 'a' and 'b', the objective is to determine the minimum number of steps required to make the string empty. In each operation, you are allowed to delete a palindromic subsequence from s. A subsequence is defined as a sequence that can be derived from another sequence by deleting zero or m ...

Finding the Kth Node from the End of a Linked List To locate the kth node from the end efficient, use two pointers—fast and slow. Advance the fast pointer by k steps first. Then move both pointers forward until fast reaches the end. At this point, slow will be pointing to the desired node. int kthToLast(struct ListNode* head, int k) { struc ...

Given a string text, the objective is to locate longest contiguous substring that reads the same forward and backward. Constraints: 1 <= text.length <= 1000 text consists of alphanumeric English characters only. Dynamic Programming Approahc 1. State Definition Define a 2D table is_palindrome[i][j] where i and j are indices. The value i ...

39. Combination Sum The key insight for this problem is understanding how elements can be reused during the search process. When recursively exploring combinations, each element can be selected multiple times since we continue searching from the current index rather than moving to the next one. Consider the tree structure: after selecting an el ...

Problem Statement Given a string of length (n), find the length of the longest palindromic substring where (n \le 10^5). Brute-Force Approach A straightforward method involves iterating through each position as a potential center and expanding outward in both directions to check for palindromes. Taking the maximum length among all centers yield ...