【JAVA、C++】LeetCode 020 Valid Parentheses

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 "([)]"…

【JAVA、C++】LeetCode 022 Generate Parentheses

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:…

【JAVA、C++】LeetCode 005 Longest Palindromic Substring

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…

【JAVA、C++】LeetCode 002 Add Two Numbers

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 ->…

【JAVA、C++】LeetCode 019 Remove Nth Node From End of List

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…

【JAVA、C++】LeetCode 010 Regular Expression Matching

Implement regular expression matching with support for '.' and '*'. '.' Matches any single character. '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). The function prototype should be…

【JAVA、C++】 LeetCode 008 String to Integer (atoi)

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…

【JAVA、C++】LeetCode 007 Reverse Integer

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=…

【JAVA、C++】LeetCode 006 ZigZag Conversion

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…

【JAVA、C++】LeetCode 004 Median of Two Sorted Arrays

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…

【JAVA、C++】LeetCode 003 Longest Substring Without Repeating Characters

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…

【JAVA、C++】LeetCode 001 Two Sum

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…

【JAVA、C++】LeetCode 021 Merge Two Sorted Lists

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…

【JAVA、C++】LeetCode 018 4Sum

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…

【JAVA、C++】LeetCode 017 Letter Combinations of a Phone Number

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…

【JAVA、C++】LeetCode 016 3Sum Closest

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…

【JAVA、C++】LeetCode 015 3Sum

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…

【JAVA、C++】LeetCode 014 Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings. 解题思路: 老实遍历即可,注意边界条件: JAVA实现: static public String longestCommonPrefix(String[] strs) { if (strs.length == 0) return ""; for (int i = 0; i < strs[0].length(…

【JAVA、C++】LeetCode 013 Roman to Integer

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…

【JAVA、C++】LeetCode 012 Integer to Roman

Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999. 本题思路比较简单,难度主要集中在罗马数字本身,直接贴代码. 思路一,从高位开始: JAVA: static public String intToRoman(int number) { int[] values = { 1000, 900, 500, 400, 100, 90, 50…

【JAVA、C++】LeetCode 011 Container With Most Water

Given n non-negative integers a1, a2, ..., an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find two lines, which together with x-axis forms a containe…