easy

ProblemYou are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: 123456Input: n = 2Output: 2Explanation: There are two ways to climb to the top.1. 1 step + 1 step2. 2 steps Example 2: 1234567Input: n = 3Output: 3Explanation: There are three ways to climb to the top.1. 1 step + 1 step + 1 step2. 1 step + 2 steps3. 2 steps + 1 step Constraints: 1 <= n <= 45 Solve用一般的**fibona ...

ProblemGiven the root of a binary tree, invert the tree, and return its root. Example 1: 123Input: root = [4,2,7,1,3,6,9]Output: [4,7,2,9,6,3,1] Example 2: 123Input: root = [2,1,3]Output: [2,3,1] Example 3: 123Input: root = []Output: [] Constraints: The number of nodes in the tree is in the range [0, 100]. 100 <= Node.val <= 100 Solve1234567891011121314151617181920# Definition for a binary tree node.# class TreeNode:# def __init__(self, val=0, left=None, right=None):# se ...

ProblemYou 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 this transaction. If you cannot achieve any profit, return 0. Example 1: 12345Input: prices = [7,1,5,3,6,4]Output: 5Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.Note that buyi ...

#ProblemWrite a function to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "". Example 1: 123Input: strs = ["flower","flow","flight"]Output: "fl" Example 2: 123Input: strs = ["dog","racecar","car"]Output: ""Explanation: There is no common prefix among the input strings. Solve1234567891011121314class Solution: def longestCommonPref ...

#ProblemGiven an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k, to get accepted, you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not import ...

#ProblemYou are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function, but instead be stored inside the array nums1. To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged, and the last ...