shirley的专栏

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402. 移掉 K 位数字（中等）我们从一个简单的问题入手，识别一下这种题的基本形式和套路，为之后的三道题打基础。题目描述给定一个以字符串表示的非负整数 num，移除这个数中的 k 位数字，使得剩下的数字最小。注意:num 的长度小于 10002 且 ≥ k。num 不会包含任何前导零。示例 1 :输入: num = "1432219", k = 3输出: "1219"解释: 移除掉三个数字 4, 3, 和 2 形成一个新的最小的数字 1219。示例 2 :输..

Given an array of integers that is alreadysorted in ascending order, find two numbers such that they add up to a specific target number.The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must b.

Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.An example is the root-to-leaf path1->2->3which represents the number123.Find the total sum of all root-to-leaf numbers.Note:A leaf is a no...

Given an unsorted array of integers, find the length of longest increasing subsequence.Example:Input: [10,9,2,5,3,7,101,18]Output: 4 Explanation: The longest increasing subsequence is [2,3,7,101], therefore the length is 4. Note:There may be mo

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.Note:For the purpose of this problem, we define empty string as valid palindrome.Example 1:Input: "A man, a plan, a canal: Panama"Output: .

You are given a binary tree in which each node contains an integer value.Find the number of paths that sum to a given value.The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to chil

Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.The length of path between two nodes is represented by the number of edges between them.Example 1:

Say you have an arraypricesfor which theithelement is the price of a given stock on dayi.Design an algorithm to find the maximum profit. You may complete as many transactions as you like (i.e., buy one and sell one share of the stock multiple times)...

Say you have an array for which theithelement is the price of a given stock on dayi.If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.Note t...

GivennumBottlesfull water bottles, you can exchangenumExchangeempty water bottles for one full water bottle.The operation of drinking a full water bottle turns it into an empty bottle.Return themaximumnumber of water bottles you candrink.Ex...

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.If the fractional part is repeating, enclose the repeating part in parentheses.If multiple answers are possible, just return any of them.

Compare two version numbersversion1andversion2.Ifversion1>version2return1;ifversion1<version2return-1;otherwise return0.You may assume that the version strings are non-empty and contain only digits and the.character.The.charac...

题目：A peak element is an element that is greater than its neighbors.Given an input arraynums, wherenums[i] ≠ nums[i+1], find a peak element and return its index.The array may contain multiple peaks, in that case return the index to any one of the pe..

Write a program to find the node at which the intersection of two singly linked lists begins.For example, the following two linked lists:begin to intersect at node c1.Example 1:Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,6,1,8,4,5

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.(i.e., [0,1,2,4,5,6,7]might become [4,5,6,7,0,1,2]).Find the minimum element.The array may contain duplicates.Example 1:Input: [1,3,5]Output: 1...

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.(i.e., [0,1,2,4,5,6,7]might become [4,5,6,7,0,1,2]).Find the minimum element.You may assume no duplicate exists in the array.Example 1:Input: [3,4,5...

Given an integer arraynums, find the contiguous subarray within an array (containing at least one number) which has the largest product.Example 1:Input: [2,3,-2,4]Output: 6Explanation:[2,3] has the largest product 6.Example 2:Input: [-2,0,-1..

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 trailin...

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) -- Push element x onto stack. pop() -- Removes the element on top of the stack. top() -- Get the top element. getMin() -- Retrieve the minimum ele

Given a binary strings(a string consisting only of '0' and '1's).Return the number of substrings with all characters 1's.Since the answermay be too large,return it modulo10^9 + 7.Example 1:Input: s = "0110111"Output: 9Explanation: There ...

Given an array of integersnums.A pair(i,j)is calledgoodifnums[i]==nums[j]andi<j.Return the number ofgoodpairs.Example 1:Input: nums = [1,2,3,1,1,3]Output: 4Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-inde...

Alice and Bob take turns playing a game, with Alice starting first.Initially, there arenstones in a pile. On each player's turn, that player makes amoveconsisting of removinganynon-zerosquare numberof stones in the pile.Also, if a player canno...

题目：Given an arraynums, you are allowed to choose one element ofnumsand change it by anyvalue in one move.Return the minimum difference between the largest and smallest value ofnumsafter perfoming at most 3 moves.Example 1:Input: nums = [5...

题目：Given the arraynumsconsisting ofnpositive integers. You computed the sum of all non-empty continous subarrays fromthe array and then sort them in non-decreasing order, creating a new array ofn * (n + 1) / 2numbers.Return the sum of the number...

题目：Given adatestring in the formDay Month Year, where:Dayis in the set{"1st", "2nd", "3rd", "4th", ..., "30th", "31st"}. Monthis in the set{"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"}. Yearis in the ran......

题目：There is a room withnbulbs, numbered from0ton-1,arranged in a row from left to right. Initially all the bulbs areturned off.Your task is to obtain the configuration represented bytargetwheretarget[i]is '1' if the i-th bulb is turned on an...

题目：Given a stringsand an integer arrayindicesof thesame length.The stringswill be shuffled such that the character at theithposition moves toindices[i]in the shuffled string.Returnthe shuffled string.Example 1:Input: s = "codeleet...

题目：Given a binary tree, return thepostordertraversal of its nodes' values.Example:Input:[1,null,2,3] 1 \ 2 / 3Output:[3,2,1]Follow up:Recursive solution is trivial, could you do it iteratively?解法一：递归法/** * Definiti...

题目：Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.For example, given the following triangle[ [2], [3,4], [6,5,7], [4,1,8,3]]The minimum path sum from top t

Given a non-negativeindexkwherek≤33, return thekthindex row of the Pascal's triangle.Note that the row index starts from0.Example:Input: 3Output: [1,3,3,1]Follow up:Could you optimize your algorithm to use onlyO(k) extra space?方法...

Given a non-negative integernumRows, generate the firstnumRowsof Pascal's triangle.Example:Input: 5Output:[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]代码如下：class Solution {public: vector<vector<int>> gener...

题目：Given a binary treestruct Node { int val; Node *left; Node *right; Node *next;}Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set toNULL.Initially, all next poin.

题目：You are given aperfect binary treewhereall leaves are on the same level, and every parent has two children. The binary tree has the following definition:struct Node { int val; Node *left; Node *right; Node *next;}Populate each next p...

Given a stringSand a stringT, count the number of distinct subsequences ofSwhich equalsT.A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the rela...

题目：Given a binary tree, return thepreordertraversal of its nodes' values.Example:Input:[1,null,2,3] 1 \ 2 / 3Output:[1,2,3]Follow up:Recursive solution is trivial, could you do it iteratively?方法一：递归代码如下：/** * Def...

题目：把二叉树转换为链表Given a binary tree, flatten it to a linked list in-place.For example, given the following tree: 1 / \ 2 5 / \ \3 4 6The flattened tree should look like:1 \ 2 \ 3 \ 4 \ 5

题目：Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.Note:A leaf is a node with no children.Example:Given the below binary tree andsum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ ..

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 andsum = 22, 5 ..