pengyu2003

摘要： There areNchildren 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 mu 阅读全文

摘要： Given an array of integers, every element appearstwiceexcept for one. Find that single one.和上一题比这题就是渣。class Solution {public: int singleNumber(int A[], int n) { if(A == NULL)return 0; int re = 0; for(int i = 0 ; i < n ;i++)re ^= A[i]; return re; }}; 阅读全文

摘要： Given an array of integers, every element appearsthreetimes except for one. Find that single one.Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?本题最好理解版本有的数字出现3次，个别出现1次，因此每出现3次就可以归零了。我们用三个量分别记录出现1次、2次、3次（其实就是0次）的位，分别为x1,x2,x3.某一位出现1次，可能之 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.这题貌似见过，大概是编程之美之类吧。复习一下深拷贝和浅拷贝的区别：深拷贝保存了指针指向的内容，二浅拷贝应对指针指示给指针赋值。所以对于有指针的地方，浅拷贝非常不安全。这段代码用了2个栈，感觉很不效率，空间O(n)。有个空间O（1）的。/** * Definition for 阅读全文

摘要： Given a stringsand a dictionary of wordsdict, determine ifscan be segmented into a space-separated sequence of one or more dictionary words.For example, givens="leetcode",dict=["leet", "code"].Return true because"leetcode"can be segmented as"leet code&quo 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?更简单的环题/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public: bool has... 阅读全文

摘要： Given a linked list, return the node where the cycle begins. If there is no cycle, returnnull.Follow up:Can you solve it without using extra space?老题，没难度。/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * ... 阅读全文

摘要： Given a singly linked listL: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}.本题 O（n）空间时间做完，但实际有O（1）的做法。那个办法是把后半部分翻转，然后merge一下就可以了。/** * Definition for singly-linked list. * struct 阅读全文

摘要： Given a binary tree, return thepreordertraversal of its nodes' values.For example:Given binary tree{1,#,2,3}, 1 \ 2 / 3return[1,2,3].此题之前和文清讨论过，一次过了。但是总体难度上，比后续迭代简单不少。/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * ... 阅读全文

摘要： Given a binary tree, return thepostordertraversal 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?递归版本就不写了，那个没难度。迭代的方法，利用一个栈。左子树一律进栈。当没有左子树的情况出现时，再考虑又子树。由于访问过的点可能也存在左子树和右子树，所以用一个last标记刚刚... 阅读全文