lly0_0

题目： Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999. 分析：罗马数字，转到阿拉伯数字是相当有规律的。比如9 -- IX， 90 -- XC， 99  -- XCIX 思路：map形式，将所有特殊的都存储起来

题目： Given a list, rotate the list to the right by k places, where k is non-negative. For example: Given 1->2->3->4->5->NULL and k = 2, return 4->5->1->2->3->NULL.分析： 将后面的k个node旋转到链表的开头。若k大于链表的长度，则

题目： Reverse a linked list from position m to n. Do it in-place and in one-pass. For example: Given 1->2->3->4->5->NULL, m = 2 and n = 4, return 1->4->3->2->5->NULL. Note: Given m, n satisfy the f

题目： Sort a linked list in O(n log n) time using constant space complexity.分析： O(n log n)有归并排序，快速排序和堆排序。针对链表，采用归并排序是比较合理的。快排在最坏的情况，复杂度是O(n^2)。思路：难点在于寻找链表的中点。代码： ListNode* sortList(ListNode* head) {

题目： Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path. Note: You can only move either down or right

题目: Given a singly linked list L: L0→L1→…→Ln-1→Ln, reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→… You must do this in-place without altering the nodes’ values. For example, Given {1,2,3,4}, reorder it to

题目：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. 这个问题，跟LCS的解题思路上

题目： Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. For example, Given 1->2->3->3->4->4->5, return 1->2->5. Given 1->

题目： Sort a linked list using insertion sort.分析： 插入排序。代码1：/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NU

题目： Given a singly linked list L: L0→L1→…→Ln-1→Ln, reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→… You must do this in-place without altering the nodes’ values. For example, Given {1,2,3,4}, reorder it to

题目: Given 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 nodes in each

题目： Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.分析： 将排好序的链表，转为平衡二叉搜索树。思路： 链表的中间那个node是树的根节点，前面是左子树，后面是右子树。以此，不断递归就可以得到平衡二叉树。时间复杂度是O（N

题目： Find the contiguous subarray within an array (containing at least one number) which has the largest sum. For example, given the array [−2,1,−3,4,−1,2,1,−5,4], the contiguous subarray [4,−1,2,1]

题目： Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclusive. For example, given the range [5, 7], you should return 4. Credits: Special

题目： Write a program to find the n-th ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first

题目： Given a linked list, swap every two adjacent nodes and return its head. For example, Given 1->2->3->4, you should return the list as 2->1->4->3. Your algorithm should use only constant space. Y

题目： Given a sorted linked list, delete all duplicates such that each element appear only once. For example, Given 1->1->2, return 1->2. Given 1->1->2->3->3, return 1->2->3.分析： 在一个链表中，将重复val的node去掉

题目： Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999. 罗马数字： ‘I’ -- 1， ‘V’ -- 5， ‘X’ -- 10， ‘L‘ -- 50， ’C‘ -- 100， ’D‘ -- 500， ’M‘

题目： Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this in place wi

题目： Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. The Sudoku board could be partially filled, where empty cells are filled with the character ‘.’ A partially filled sud

题目： Given two binary strings, return their sum (also a binary string). For example, a = “11” b = “1” Return “100”.、分析： 就是这么简单，二进制相加代码：string addBinary(string a, string b) { string str = "

题目： Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array. For example, Given nums = [0, 1, 3] return 2. Note: Your algorithm should ru

题目： 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) mu

题目： 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 exa

题目： 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, w

题目： 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. Note: Elements in

题目： 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 tw

题目： Write a function to find the longest common prefix string amongst an array of strings.分析： 一堆string里面，找到大家共有的从头部开始的字串思路： 遍历，复杂度O（N）。每次记下当前最长的字串，然后跟新的一个string比较，获取当前的最长字串。代码：string longestCommonPr

题目： Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where “adjacent” cells are those horizontally or vertical

题目： 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, t

题目： Remove all elements from a linked list of integers that have value val. Example Given: 1 –> 2 –> 6 –> 3 –> 4 –> 5 –> 6, val = 6 Return: 1 –> 2 –> 3 –> 4 –> 5分析： 删除链表中顶点值为val的node思路： 遍历链表，遇到满足

题目： Description: Count the number of prime numbers less than a non-negative number, n. Credits: Special thanks to @mithmatt for adding this problem and creating all test cases.分析【引自：Leetcode Hint】：