pengyu2003

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

摘要： Sort a linked list using insertion sort.指针的初始值设置有问题，梁旭两天童颜的错误了。/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public: ListNode *insertionSortList(ListNode *head) { if(hea... 阅读全文

摘要： Sort a linked list inO(nlogn) time using constant space complexity.逻辑正确，尾指针没有置空，调了好久……/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public: ListNode *sortList(ListNode *head) {... 阅读全文

摘要： Evaluate the value of an arithmetic expression inReverse Polish Notation.Valid operators are+,-,*,/. Each operand may be an integer or another expression.Some examples: ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 ["4", "13&qu 阅读全文

摘要： Given an input string, reverse the string word by word.For example,Given s = "the sky is blue",return "blue is sky the".click to show clarification.Clarification:What constitutes a word?A sequence of non-space characters constitutes a word.Could the input string contain leading o 阅读全文

摘要： Implementint sqrt(int x).Compute and return the square root ofx.此题看着简单，实则坑爹啊！！！！！首先，关于平方，int是不够用的。其次，二分法肯定好用，但是，最终的结果怎么取？原则上取小于等于的最近整数。但是mid的计算可能会更改这个数，所以需要调整一下。class Solution {public: int sqrt(int x) { long long left = 0; long long right = x; long long mid = left + (right - lef... 阅读全文

摘要： Given a collection of numbers that might contain duplicates, return all possible unique permutations.For example,[1,1,2]have the following unique permutations:[1,1,2],[1,2,1], and[2,1,1].class Solution {public: vector > re; vector > permuteUnique(vector &num) { map m; int size = ... 阅读全文

摘要： Given a collection of intervals, merge all overlapping intervals.For example,Given[1,3],[2,6],[8,10],[15,18],return[1,6],[8,10],[15,18].排序/** * Definition for an interval. * struct Interval { * int start; * int end; * Interval() : start(0), end(0) {} * Interval(int s, int e) : start(... 阅读全文