cfylove的专栏

题目内容Follow up for N-Queens problem.Now, instead outputting board configurations, return the total number of distinct solutions.题目分析n皇后问题，找出所有的可行解。通过本方法，没有记录皇后的坐标代码public class Solution {private final

题目内容 Given n, how many structurally unique BST’s (binary search trees) that store values 1…n?For example, Given n = 3, there are a total of 5 unique BST’s.1 3 3 2 1\ /

题目内容 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 run

题目内容 Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 题目分析 给定一个排好序的数组，然后将其转换成最平衡的二叉查找树。 根据二叉查找树的特点，左孩子都小于父节点，右孩子都大于父节点。所以，可以直接利用排序好的数组，取数组中间下标的值，不断作

题目内容 Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].Solve it without division and in O(n

题目内容 Given two arrays, write a function to compute their intersection.Example: Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].Note:Each element in the result should appear as many times a

题目内容 Given a binary tree, return the postorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3},1 \ 2 / 3return [3,2,1].Note: Recursive solution is trivial,

题目内容 Say you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy o

题目内容 Say you have an array for which the ith element is the price of a given stock on day i.If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock)

题目内容 Given a non-empty array of integers, return the k most frequent elements.For example, Given [1,1,1,2,2,3] and k = 2, return [1,2].Note:You may assume k is always valid, 1 ≤ k ≤ number of unique

题目描述 Write a function that takes a string as input and returns the string reversed.Example: Given s = “hello”, return “olleh”. 题目分析 这是一道水题，唯一的坑点是可能字符串 s 过长。如果定义变量 String ss+=s.charAt(n)，这样的写法会造成超时。s

题目内容 Given an integer, write a function to determine if it is a power of two. 题目分析 判断一个数是不是2的冥。 只要对该数减一，然后&操作就可以了。 例如 8=1000,8-1=0111,1000&0111=0；即可知道该数是不是2的冥了。public class Solution { public bo

题目内容Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.Example: Given n = 2, return 91. (The answer should be the total numbers in the range of 0 ≤ x < 100, exc

题目内容 Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.Example: Given a = 1 and b = 2, return 3.Credits: Special thanks to @fujiaozhu for adding this pro

题目内容 Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate numbe

题目内容You 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 that adjacent ho

题目内容 Write a function that takes a string as input and reverse only the vowels of a string.Example 1: Given s = “hello”, return “holle”.Example 2: Given s = “leetcode”, return “leotcede”. 题目分析 翻转字符

题目内容Given a binary tree, return the preorder traversal of its nodes’ values. For example: Given binary tree {1,#,2,3}, 1 \ 2 / 3return [1,2,3].Note: Recursive solution

题目内容 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. You

题目内容 Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note: You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold addi

题目内容 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.题目分析 将两个排序好的链表，归并成一个新排序好的链表。 比较两个链表的最前端的值，然后比较加入新链表，

题目内容 Given an array of integers, every element appears three times except for one. Find that single one.Note: Your algorithm should have a linear runtime complexity. Could you implement it without u

题目内容 Given a binary tree, return the inorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3},1 \ 2 / 3return [1,3,2].Note: Recursive solution is trivial, c

题目内容 Write a function to delete a node (except the tail) in a singly linked list, given only access to that node.Supposed the linked list is 1 -> 2 -> 3 -> 4 and you are given the third node with val

题目描述 Invert a binary tree. 题目分析 将二叉树翻转，通过不断递归实现二叉树的翻转。/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNo

题目内容 Implement the following operations of a queue using stacks.push(x) -- Push element x to the back of queue.pop() -- Removes the element from in front of queue.peek() -- Get the front element.e

题目内容 Write a program to check whether a given number is an ugly number.Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly sinc

题目内容 Given an array nums, write a function to move all 0’s to the end of it while maintaining the relative order of the non-zero elements.For example, given nums = [0, 1, 0, 3, 12], after calling you

题目描述 给出一棵二叉树，求二叉树的宽度。 解析 二叉树的宽度：空的二叉树的宽度为0，非空二叉树的宽度为各层结点个数的最大值。 依然用BFS。/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode rig

Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.You may assume that the array is non-empty and the majority element always

题目：Given an array of integers, every element appears twice except for one. Find that single one.Note:Your algorithm should have a linear runtime complexity. Could you implement it without usin

题目You are playing the following Nim Game with your friend: There is a heap of stones on the table, each time one of you take turns to remove 1 to 3 stones. The one who removes the last stone will be th

题目内容 Given two strings s and t, write a function to determine if t is an anagram of s.For example, s = “anagram”, t = “nagaram”, return true. s = “rat”, t = “car”, return false.Note: You may assume

题目内容 You are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? 题目分析 我们假设，最后一步完成爬台阶。那么就有两种爬法出

题目内容 Given an array of numbers nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once.For example:Given nums

题目内容 Given a positive integer n, break it into the sum of at least two positive integers and maximize the product of those integers. Return the maximum product you can get.For example, given n = 2, r

题目内容 Given a linked list, return the node where the cycle begins. If there is no cycle, return null. 题目分析 在141题的基础上，加入了寻找出了环的起点位置，如果有环找出起点，没有环返回null。 找出环的起点，当找到确定有环以后，讲fast标记回head结点，然后步长调整为1，当再次与

题目内容 Given a linked list, determine if it has a cycle in it. 题目分析 判断一个链表是否有环， 设置fast和slow两个flag，当fast和slow相遇以后就证明有环 具体证明 点击这里/** * Definition for singly-linked list. * class ListNode { *

题目内容 Given two binary trees, write a function to check if they are equal or not.Two binary trees are considered equal if they are structurally identical and the nodes have the same value. 题目分析 递归调用函

题目内容 Related to question Excel Sheet Column TitleGiven a column title as appear in an Excel sheet, return its corresponding column number.For example:A -> 1B -> 2C -> 3...Z -> 26AA -> 27AB -> 28