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Implement a basic calculator to evaluate a simple expression string. The expression string contains only non-negative integers, ‘+’, ‘-’, ‘*’, ‘/’ operators, and open ‘(’ and closing parentheses ‘)’. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231, 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval()....

You are given a string expression representing a Lisp-like expression to return the integer value of. The syntax for these expressions is given as follows. -An expression is either an integer, let expression, add expression, mult expression, or an assigned variable. Expressions always evaluate to a single integer. (An integer could be positive or negative.) A let expression takes the form “(let v1 e1 v2 e2 … vn en expr)”, where let is always the string “let”, then there are one or more pairs of alternating variables and expressions, meaning that the first variable v1 is assigned the value of the expression e1, the second variable v2 is assigned the value of the expression e2, and so on sequentially; and then the value of this let expression is the value of the expression expr....

Given a string s, return all the palindromic permutations (without duplicates) of it. You may return the answer in any order. If s has no palindromic permutation, return an empty list. 1 2 3 4 5 6 7 8 9 Example 1: Input: s = "aabb" Output: ["abba","baab"] Example 2: Input: s = "abc" Output: [] Constraints: 1 <= s.length <= 16 s consists of only lowercase English letters. Solution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 class Solution { public List<String> generatePalindromes(String s) { Set<String> res = new HashSet<>(); int[] freq = new int[256]; int count = 0; for (char c : s....

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters. Letters are case sensitive, for example, “Aa” is not considered a palindrome here. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Example 1: Input: s = "abccccdd" Output: 7 Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7....

Given a string s, return true if a permutation of the string could form a palindrome. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Example 1: Input: s = "code" Output: false Example 2: Input: s = "aab" Output: true Example 3: Input: s = "carerac" Output: true Constraints: 1 <= s.length <= 5000 s consists of only lowercase English letters. Solution 1 2 3 4 5 6 7 8 9 10 11 12 13 class Solution { public boolean canPermutePalindrome(String s) { int[] freq = new int[256]; for (char c: s....

We can shift a string by shifting each of its letters to its successive letter. For example, “abc” can be shifted to be “bcd”. We can keep shifting the string to form a sequence. For example, we can keep shifting “abc” to form the sequence: “abc” -> “bcd” -> … -> “xyz”. Given an array of strings strings, group all strings[i] that belong to the same shifting sequence. You may return the answer in any order....

A parentheses string is valid if and only if: It is the empty string, It can be written as AB (A concatenated with B), where A and B are valid strings, or It can be written as (A), where A is a valid string. You are given a parentheses string s. In one move, you can insert a parenthesis at any position of the string. For example, if s = “()))”, you can insert an opening parenthesis to be “(()))” or a closing parenthesis to be “())))”....

Given two strings s and t, return true if they are both one edit distance apart, otherwise return false. A string s is said to be one distance apart from a string t if you can: Insert exactly one character into s to get t. Delete exactly one character from s to get t. Replace exactly one character of s with a different character to get t. 1 2 3 4 5 Example 1: Input: s = "ab", t = "acb" Output: true Explanation: We can insert 'c' into s to get t....

Given a string queryIP, return “IPv4” if IP is a valid IPv4 address, “IPv6” if IP is a valid IPv6 address or “Neither” if IP is not a correct IP of any type. A valid IPv4 address is an IP in the form “x1.x2.x3.x4” where 0 <= xi <= 255 and xi cannot contain leading zeros. For example, “192.168.1.1” and “192.168.1.0” are valid IPv4 addresses but “192.168.01.1”, while “192.168.1.00” and “192....

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s, return true if it is a palindrome, or false otherwise. 1 2 3 4 5 Example 1: Input: s = "A man, a plan, a canal: Panama" Output: true Explanation: "amanaplanacanalpanama" is a palindrome....

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string. Note: You must not use any built-in BigInteger library or convert the inputs to integer directly. 1 2 3 4 5 6 7 8 9 Example 1: Input: num1 = "2", num2 = "3" Output: "6" Example 2: Input: num1 = "123", num2 = "456" Output: "56088" Constraints:...

Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer (similar to C/C++’s atoi function). The algorithm for myAtoi(string s) is as follows: Read in and ignore any leading whitespace. Check if the next character (if not already at the end of the string) is ‘-’ or ‘+’. Read this character in if it is either. This determines if the final result is negative or positive respectively....

Given two strings s and t of length N, find the maximum number of possible matching pairs in strings s and t after swapping exactly two characters within s. A swap is switching s[i] and s[j], where s[i] and s[j] denotes the character that is present at the ith and jth index of s, respectively. The matching pairs of the two strings are defined as the number of indices for which s[i] and t[i] are equal....

Given two string arrays word1 and word2, return true if the two arrays represent the same string, and false otherwise. A string is represented by an array if the array elements concatenated in order forms the string. 1 2 3 4 5 6 7 8 Example 1: Input: word1 = ["ab", "c"], word2 = ["a", "bc"] Output: true Explanation: word1 represents string "ab" + "c" -> "abc" word2 represents string "a" + "bc" -> "abc" The strings are the same, so return true....

1360. Number of Days Between Two Dates Write a program to count the number of days between two dates. The two dates are given as strings, their format is YYYY-MM-DD as shown in the examples. 1 2 3 4 5 6 7 8 9 Example 1: Input: date1 = "2019-06-29", date2 = "2019-06-30" Output: 1 Example 2: Input: date1 = "2020-01-15", date2 = "2019-12-31" Output: 15 Constraints: The given dates are valid dates between the years 1971 and 2100....