386. 字典序排数 给定一个整数 n, 返回从 1 到 n 的字典顺序. 例如, 给定 n =1 3,返回 [1,10,11,12,13,2,3,4,5,6,7,8,9] . 请尽可能的优化算法的时间复杂度和空间复杂度. 输入的数据 n 小于等于 5,000,000. 通过次数6,670提交次数9,748 class Solution { void reversalTree2(int root, int n, ArrayList<Integer> list) { list.add(root)

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring. 解题思路一: 暴力枚举 共N^2量级个子串(从下标零开始),每次检查需一个for循环,等于是3重for循环,时间复杂度O(n^3) 解题思路二: 动态

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999. 解题思路: 类似上题,方法多多,本题直接给出上题中字典匹配的代码: JAVA实现: static public int romanToInt(String s) { int num=0; String Roman[][] = { {"", "I", &q

import java.util.ArrayList; import java.util.HashMap; import java.util.Map; import java.util.Set; public class list_map { //列表的使用方法 public static void list_test(){ ArrayList<Object> array = new ArrayList<Object>(); array.add("八戒你瘦了!"

按位操作符只能用于整数基本数据类型中的单个bit中,操作符对应表格: Operator Description & 按位与(12345&1=1,可用于判断整数的奇偶性) | 按位或 ^ 异或(同假异真) ~ 非(一元操作符) &=,|=,^= 合并运算和赋值 <<N 左移N位,低位补0 >>N 右移N位,(正数:高位补0,负数高位补1) >>>N 无符号右移(无论正负数,高位皆补0) <<=,>>=,>>

标准Java库只包含Dictionary的一个变种,名为:Hashtable.(散列表) Java的散列表具有与AssocArray相同的接口(因为两者都是从Dictionary继承来的).但有一个方面却反映出了差别:执行效率.若仔细想想必须为一个get()做的事情,就会发现在一个Vector里搜索键的速度要慢得多.但此时用散列表却可以加快不少速度.不必用冗长的线性搜索技术来查找一个键,而是用一个特殊的值,名为"散列码".散列码可以获取对象中的信息,然后将其转换成那个对象"相

Implement atoi to convert a string to an integer. Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases. Notes: It is intended for this problem to be spe

Reverse digits of an integer. Example1: x = 123, return 321 Example2: x = -123, return -321 解题思路:将数字翻转并不难,可以转成String类型翻转,也可以逐位翻转,本题涉及到的主要是边界和溢出问题,使用Long或者BigInteger即可解决. 题目不难: JAVA实现如下: public class Solution { static public int reverse(int x) { if(x=

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: "PAHNAPLSII

There are two sorted arrays nums1 and nums2 of size m and n respectively. Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). 解题思路: 由于要求时间复杂度O(log (m+n))所以几乎可以肯定是递归和分治的思想. <算法导论>里有找两个数组第K小数的算法,时间复杂度为O(lo

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest subst

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. Input: (2 -> 4 -> 3) + (5 -> 6 ->

Given an array of integers, 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 be less than index2. Please note that

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is: "((()))", "(()())", "(())()", "()(())", "()()()" 解题思路一:

  Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists. 解题思路: 新建一个ListNode进行存储即可,JAVA实现如下: static public ListNode mergeTwoLists(ListNode l1, ListNode l2) { ListNo

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]"

Given a linked list, remove the nth node from the end of list and return its head. For example, Given linked list: 1->2->3->4->5, and n = 2. After removing the second node from the end, the linked list becomes 1->2->3->5. Note: Given

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target. 解题思路一: 四路夹逼,C++: class Solution { public: vector<vector<int> > fou

Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. 解题思路: 思路一: 使用DFS算法,JAVA实现如下: static String[] alpha = new String[] { " &q

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution. For example, given array S = {-1 2

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. Note: Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c) The solut