cfanr

题目 Given a linked list, determine if it has a cycle in it. Follow up: Can you solve it without using extra space? 解答 首先要注意空链表不成环;不能开额外的空间，即空间复杂度是o(1),可采用“快慢指针”查检查链表是否含有环，如果在快的指针能够追上慢的指针，则有环，否

题目 Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find

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 spac

题目 Sort a linked list using insertion sort. 解答 链表无法像数组那样从后往前依次比较插入，只能从前往后；在链表首部添加一个哨兵可以稍微简化下代码，代码如下： /** * Definition for singly-linked list. * public class ListNode { * int val; *

题目 Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example: Given the below binary tree