七年之后

摘要： Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).For example: Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7return its zigzag level order traversal as:[ [... 阅读全文

摘要： Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).For example: Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7return its level order traversal as:[ [3], [9,20], [15,7]]confused what "{1,#,2,3}" means? > rea. 阅读全文

摘要： There are N children standing in a line. Each child is assigned a rating value.You are giving candies to these children subjected to the following requirements:Each child must have at least one candy.Children with a higher rating get more candies than their neighbors.What is the minimum candies you 阅读全文

摘要： 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 using extra memory?思考：参考这里。class Solution {public: int singleNumber(int A[], int n) { // IMPORTANT... 阅读全文

摘要： 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 using extra memory?思考：位运算。class Solution {public: int singleNumber(int A[], int n) { // IMPORTANT: Pleas... 阅读全文

摘要： 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.思考：先进行单链表复制，在定义random指针，每个结点的random指针都要遍历一次链表，时间复杂度为O(n2)。/** * Definition for singly-linked list with a random pointer. * struct RandomLi 阅读全文

摘要： 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?思考：第一步：设环长为len，快慢指针q、p相遇时，q比p多走了k*len。 第二部：p先走k*len步，p，q一起走每次一步，相遇时p比q多走了一个环距离，此时q就是环开始结点。通过分析AC的感觉真好！class Solution {public: ListNode *detectCycle(... 阅读全文

摘要： Given a linked list, determine if it has a cycle in it.Follow up: Can you solve it without using extra space?思考：快慢指针，快指针一次走两步，慢指针一次一步。若快指针跟慢指针指向同一个结点，则有环。若快指针到达链表末尾即指向NULL，说明没有环。/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : ... 阅读全文

摘要： 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 {1,4,2,3}.思考：[微软原题点击]。O(n2)方法这里就不贴了。因为每次要插入的结点都是尾结点，从头结点开始寻找时间都花费在查询上。题意说只可以改变.next，这算是一个提示吧。我们可以翻转待插入链表结点 阅读全文

摘要： 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, could you do it iteratively?思考：原思路是为每个节点增加一个标记。这个思路先序遍历不要标记，因为当前访问结点直接出栈，不用看是否访问过。不过此思路redefinition of 'struct... 阅读全文