chfe910的专栏

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. Inpu

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.这类问题非常适合用递归做，递归思路如下：前序遍历的第一个节点必然是根节点，中序遍历中根节点之前的节

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.看到这个题目感到奇怪的是为什么是“右旋”，而不是“左旋

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).这个题目比较简单，借助容器queue即可完成二叉树的层序遍历。我的C++实现代码如下：vector > levelOrder(TreeNode *

Given two sorted integer arrays A and B, merge B into A as one sorted array.Note:You may assume that A has enough space (size that is greater or equal to m + n) to hold additional elements from B.

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 su

Given two binary strings, return their sum (also a binary string).For example,a = "11"b = "1"Return "100".我的C++实现代码如下：string addBinary(string a, string b) { string sum; int c

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:Integers in each row are sorted from left to right.The first integer of each row

Given a non-negative number represented as an array of digits, plus one to the number.The digits are stored such that the most significant digit is at the head of the list.一开始我误解了题目的意思，以为是新建一个

Given numRows, generate the first numRows of Pascal's triangle.For example, given numRows = 5,Return[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]这个问题比较简单，大家的解法大同小异。时间复杂度都

Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.If the last word does not exist, return 0.Note: A word is defin

Suppose a sorted array 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

Write a program to find the node at which the intersection of two singly linked lists begins.Notes:If the two linked lists have no intersection at all, return null.The linked lists must retain t

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.Follow up:Did you use extra space?A straight forward solution using O(mn) space is probably a bad ide

Given an array and a value, remove all instances of that value in place and return the new length.The order of elements can be changed. It doesn't matter what you leave beyond the new length.方

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.Return a deep copy of the list./** * Definition for singly-linke

Given a linked list, determine if it has a cycle in it.Follow up:Can you solve it without using extra space?这个题目如果没有空间复杂度O(1)的限制，我可以想到的方法就是：遍历整个list，将每个节点的地址存入一个vector，如果发现某个节点的next的地址已经在vec

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

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

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).这个简单的问题可以这样解决：利用LeetCode[Tree]: Binary Tree Level

Given an index k, return the kth row of the Pascal's triangle.For example, given k = 3,Return [1,3,3,1].Note:Could you optimize your algorithm to use only O(k) extra space?这个问题比较简单。v

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.Follow up:Can you solve it without using extra space?这个题目跟Linked List Cycle一样，我也没有能够自己独立找到解决方法，

Given a set of distinct integers, S, return all possible subsets. Note: Elements in a subset must be in non-descending order. The solution set must not contain duplicate subsets. For exampl

Find the contiguous subarray within an array (containing at least one number) which has the largest product. For example, given the array [2,3,-2,4], the contiguous subarray [2,3] has the largest

Write a function to find the longest common prefix string amongst an array of strings.这个题目非常简单，只要弄清楚题意就可以非常快地解决，我的C++代码实现如下： string longestCommonPrefix(vector<string> &strs) { if (strs.empt

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. - to

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.这个题目首先要了解罗马数字的拼写规则（以下引自维基百科）：罗马数字共有7个，即I（1）、V（5）、X（10）、L（50）、C（100）、D（500）和M（1000）。按照下述的规则

Validate if a given string is numeric. Some examples: "0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true Note: It is intended for the problem statement to be

Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.欲了解罗马数字的拼写规则请参考：http://blog.youkuaiyun.com/chfe007/article/details/44037079C++代码实现如下： string

Given an unsorted array of integers, find the length of the longest consecutive elements sequence. For example, Given [100, 4, 200, 1, 3, 2], The longest consecutive elements sequence is [1, 2

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’s in that surrounded region. For example, X X X X X O O X

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. Calling next() will return the next smallest number in the BST. Note: next()

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

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

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

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 bu

Given a sorted array of integers, find the starting and ending position of a given target value.Your algorithm's runtime complexity must be in the order of O(log n).If the target is not found in t

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 of t

Implement int sqrt(int x). Compute and return the square root of x.这个题目适合用位操作来做，时间和空间复杂度都是O(1)。首先找到根的最高位，然后从最高位开始，依次判断各个位值是否为1。C++代码实现如下： int sqrt(int x) { int i, j, res = 0;

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. For example, Given [0,1,0,2,1,0,1,3,2,1,2,1],