Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2. Note The length of both num1 and num2 is < 5100. Both num1 and num2 contains only digits 0-9. Both num1 and num2 does not contain any leading zero. You must not use any built-in BigInteger library or convert the inputs to integer directly. Solution class Solution: def addStrings(self, num1: str, num2: str) -> str: if len(num1) < len(num2): return self.
Given an input string, reverse the string word by word. Example 1 Input: "the sky is blue" Output: "blue is sky the" Example 2 Input: " hello world! " Output: "world! hello" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3 Input: "a good example" Output: "example good a" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.
Given a complete binary tree, count the number of nodes. Note Definition of a complete binary tree from Wikipedia: In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2hnodes inclusive at the last level h. Example: Input: 1 / \ 2 3 / \ / 4 5 6 Output: 6 Solution # Definition for a binary tree node.
Given a n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order, not the kth distinct element. Example: matrix = [ [ 1, 5, 9], [10, 11, 13], [12, 13, 15] ], k = 8, return 13. Note You may assume k is always valid, 1 ≤ k ≤ n2.
Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node’s descendants. The tree s could also be considered as a subtree of itself. Example 1 Given tree s: 3 / \ 4 5 / \ 1 2 Given tree t:
On a campus represented as a 2D grid, there are N workers and M bikes, with N <= M. Each worker and bike is a 2D coordinate on this grid. Our goal is to assign a bike to each worker. Among the available bikes and workers, we choose the (worker, bike) pair with the shortest Manhattan distance between each other, and assign the bike to that worker. (If there are multiple (worker, bike) pairs with the same shortest Manhattan distance, we choose the pair with the smallest worker index; if there are multiple ways to do that, we choose the pair with the smallest bike index).
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. Note A leaf is a node with no children. Example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ \ 7 2 1 return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
Given a list of non-negative numbers and a target integer k, write a function to check if the array has a continuous subarray of size at least 2 that sums up to a multiple of k, that is, sums up to n*k where n is also an integer. Example 1 Input: [23, 2, 4, 6, 7], k=6 Output: True Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6.
Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1. Example: Given the sorted linked list: [-10,-3,0,5,9], One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST: 0 / \ -3 9 / / -10 5 Solution (recursion) # Definition for singly-linked list.
Given a file and assume that you can only read the file using a given method read4, implement a method read to read n characters. Your method read may be called multiple times. Method read4: The API read4 reads 4 consecutive characters from the file, then writes those characters into the buffer array buf. The return value is the number of actual characters read. Note that read4() has its own file pointer, much like FILE *fp in C.