Narcssus的专栏

[LeetCode]Code of Easy Problem

Problem Description[https://leetcode.com/problems/missing-number/] Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array.For example, Give

Problem DescriptionSerialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network con

Problem DescriptionGiven an array where elements are sorted in ascending order, convert it to a height balanced BST. [https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/]思路二分！！！就

Problem DescriptionGiven an array of strings, group anagrams together.For example, given: [“eat”, “tea”, “tan”, “ate”, “nat”, “bat”], Return:[ [“ate”, “eat”,”tea”], [“nat”,”tan”], [“bat”] ]

Problem DescriptionGiven a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place. https://leetcode.com/problems/set-matrix-zeroes/思路如果要用O(1)的额外空间的话，利用数组第0列和第0行来记录0的位置就好了

Problem DescriptionGiven a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.For example, given s = “leetcode”,

Problem DescriptionOne way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node’s value. If it is a null node, we record using a sentinel valu

Problem DescriptionGiven n, how many structurally unique BST’s (binary search trees) that store values 1…n? [https://leetcode.com/problems/unique-binary-search-trees/]思路DP!状态转移方程： DP[n]=DP[0]*DP[n-1

Problem DescriptionGiven a sorted positive integer array nums and an integer n, add/patch elements to the array such that any number in range [1, n] inclusive can be formed by the sum of some elements

Problem DescriptionYou are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is t

Problem DescriptionAdditive number is a string whose digits can form additive sequence.A valid additive sequence should contain at least three numbers. Except for the first two numbers, each subsequent

Problem DescriptionGiven a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.You should preserve the original relative order of the no

Problem DescriptionGiven a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined betw

Problem DescriptionGiven a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.According to the definition of LCA on Wikipedia: “The lowest common ancestor is

Problem DescriptionGiven an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.For example: Given n = 13, Return 6, because digit 1 occurred i

Problem DescriptionA robot is located at the top-left corner of a m x n grid (marked ‘Start’ in the diagram below).The robot can only move either down or right at any point in time. The robot is trying

Problem DescriptionGiven 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 p

Problem Description[https://leetcode.com/problems/binary-tree-inorder-traversal/] Given a binary tree, return the inorder traversal of its nodes’ values.思路本来刚刚做完一题想撤来着，pick one 了这个！！！ F! pick one 有毒！

Problem DescriptionGiven a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1’s in their binary representation and return them as an array. [https:

Problem Description[https://leetcode.com/problems/spiral-matrix/] Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.For example, Given the follow

Problem Description[https://leetcode.com/problems/surrounded-regions/] Given a 2D board containing ‘X’ and ‘O’, capture all regions surrounded by ‘X’.A region is captured by flipping all ‘O’s into ‘X’

Problem Description[https://leetcode.com/problems/unique-paths-ii/] Follow up for “Unique Paths”:Now consider if some obstacles are added to the grids. How many unique paths would there be?An obstacle

Problem Description[https://leetcode.com/problems/range-sum-query-2d-immutable/] Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col

Problem Description[https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/] Follow up for “Remove Duplicates”: What if duplicates are allowed at most twice?For example, Given sorted a

Problem Description[https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/] Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced B

Problem Description[https://leetcode.com/problems/next-permutation/] Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.If such arrange

Problem Description[https://leetcode.com/problems/kth-smallest-element-in-a-bst/] Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.思路既然可能找很多遍，不如直接做一个有序的数

Problem Description[https://leetcode.com/problems/triangle/] Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.思路DP hahaha,我的

Problem Description[https://leetcode.com/problems/generate-parentheses/] Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3

Problem DescriptionImplement strStr().Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. [https://leetcode.com/problems/implement-strstr/]思路其实不用K

Problem Description[https://leetcode.com/problems/implement-trie-prefix-tree/] Implement a trie with insert, search, and startsWith methods.思路没啥好说的，看代码就好惹。。Codepackage q208;import java.util.LinkedList

Problem Description[https://leetcode.com/problems/powx-n/] Implement pow(x, n).思路不明白这种题为什么会是mid的。。。Codepackage q050;public class Solution { public double myPow(double x, int n) { if (n ==

Problem Description[https://leetcode.com/problems/increasing-triplet-subsequence/] Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.Formally the

Problem Description[https://leetcode.com/problems/divide-two-integers/] Divide two integers without using multiplication, division and mod operator.If it is overflow, return MAX_INT.思路没啥好说的，最讨厌做有关int范

Problem Description[https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/] Say you have an array for which the ith element is the price of a given stock on day i.Design an algor

Problem DescriptionGiven a binary tree, flatten it to a linked list in-place. [https://leetcode.com/problems/flatten-binary-tree-to-linked-list/]思路先序遍历，然后按个保存就行了。。。 左右不分真的不利于手写代码。。。要不是调试一下就是反的了。。。Cod

Problem DescriptionGiven a string s, partition s such that every substring of the partition is a palindrome.Return all possible palindrome partitioning of s.For example, given s = “aab”, Return[

Problem DescriptionGiven an array of integers, every element appears three times except for one. Find that single one. [https://leetcode.com/problems/single-number-ii/]

Problem DescriptionGiven a 2D binary matrix filled with 0’s and 1’s, find the largest square containing all 1’s and return its area. [https://leetcode.com/problems/maximal-square/]