LouisLan的学习简记 👋🏼

题目地址 https://leetcode.com/problems/subsets-ii/ 题目描述 Given a collection of integers that might contain duplicates, nums, return all possible subsets (the power set). Note: The solution set must not contain duplicate subsets. Example: Input: [1,2,2] Output: [ [2], [1], [1,2,2], [2,2], [1,2], [] ] 思路 这道子集合之二是之前那道 Subsets 的延伸，这次输入数组允许有重复项，其他条件都不变，只需要在之前那道题解法的基础上稍加改动便可以做出来，我们先来看非递归解法，拿题目中的例子 [1 2 2] 来分析，根据之前 Subsets 里的分析可知，当处理到第一个 2 时，此时的子集合为 [], [1], [2], [1, 2]，而这时再处理第二个 2 时，如果在 [] 和 [1] 后直接加 2 会产....

题目地址 https://leetcode.com/problems/gray-code/ 题目描述 The gray code is a binary numeral system where two successive values differ in only one bit. Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0. Example 1: Input: 2 Output: [0,1,3,2] Explanation: 00 - 0 01 - 1 11 - 3 10 - 2 For a given n, a gray code sequence may not be uniquely defined. For example, [0,2,3,1] is also a valid gray code sequence....

题目地址 https://leetcode.com/problems/merge-sorted-array/ 题目描述 Given two sorted integer arrays nums1 and nums2 , merge nums2 into nums1 as one sorted array. Note: The number of elements initialized in nums1 and nums2 are m and n respectively. You may assume that nums1 has enough space (size that is greater or equal to m + n ) to hold additional elements from nums2. Example: Input: nums1 = [1,2,3,0,0,0], m = 3 nums2 = [2,5,6], n = 3 Output: [1,2,2,3,5,6] 思路 混合插入有序数组，由于两个数组都是有序的，所有只要按顺序比较大小即可。题目中说....

题目地址 https://leetcode.com/problems/scramble-string/ 题目描述 Given a string s1 , we may represent it as a binary tree by partitioning it to two non-empty substrings recursively. Below is one possible representation of s1 = "great": great / \ gr eat / \ / \ g r e at / \ a t To scramble the string, we may choose any non-leaf node and swap its two children. For example, if we choose the node "gr" and swap its two children, it produces a scrambled string "rgeat". rgeat / \ rg eat / \ / \ r g e at / \....

题目地址 https://leetcode.com/problems/partition-list/ 题目描述 Given a linked list and a value x , partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. For example, Given 1->4->3->2->5->2 and x = 3, return 1->2->2->4->3->5. 思路 这道题要求我们划分链表，把所有小于给定值的节点都移到前面，大于该值的节点顺序不变，相当于一个局部排序的问题。那么可以想到的一种解法是首先找到第一个大于或等于给定值的节点，用题目中给的例子来说就是先找到 4，然后再找小于 3 的值，每找到一个....

高等数学 1.导数定义： 导数和微分的概念 f'(x_{0}) = \lim_{\Delta x \rightarrow 0}\,\frac{f(x_{0} + \Delta x) - f(x_{0})}{\text{Δx}} （1） 或者：f'(x_{0}) = \lim_{x \rightarrow x_{0}}\,\frac{f(x) - f(x_{0})}{x - x_{0}} （2） 2.左右导数导数的几何意义和物理意义 函数f(x)在x_{0}处的左、右导数分别定义为： 左导数：{f'}_{-}(x_{0}) = \lim_{\Delta x \rightarrow 0^{-}}\,\frac{f(x_{0} + \Delta x) - f(x_{0})}{\text{Δx}} = \lim_{x \rightarrow x_{0}^{-}}\,\frac{f(x) - f(x_{0})}{x - x_{0}},(x = x_{0} + \Delta x) 右导数：{f'}_{+}(x_{0}) = \lim_{\Delta x \rightarrow 0^{+}}\,\....

题目地址 https://leetcode.com/problems/maximal-rectangle/ 题目描述 Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area. Example: Input: [ ["1","0","1","0","0"], ["1","0","1","1","1"], ["1","1","1","1","1"], ["1","0","0","1","0"] ] Output: 6 思路 此题是之前那道的 Largest Rectangle in Histogram 的扩展，这道题的二维矩阵每一层向上都可以看做一个直方图，输入矩阵有多少行，就可以形成多少个直方图，对每个直方图都调用 Largest Rectangle in Histogram 中的方法，就可以得到最大的矩形面积。那么这道题唯一要做的就是将每一层都当作直方图的底层，并向上构造整个直方图，由于题目限定了输入矩阵的字....

题目地址 https://leetcode.com/problems/largest-rectangle-in-histogram/ 题目描述 Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram. Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3]. The largest rectangle is shown in the shaded area, which has area = 10 unit. For example, Given height = [2,1,5,6,2,3], return 10. 思路 这道题让求直方图中最大的矩形，刚开始看到求极值问题以为要用 DP 来做，可是想不出递推式，只得作罢。这道题....

题目地址 https://leetcode.com/problems/remove-duplicates-from-sorted-list/ 题目描述 Given a sorted linked list, delete all duplicates such that each element appear only once. Example 1: Input: 1->1->2 Output: 1->2 Example 2: Input: 1->1->2->3->3 Output: 1->2->3 思路 这道题让我们移除给定有序链表的重复项，那么可以遍历这个链表，每个结点和其后面的结点比较，如果结点值相同了，只要将前面结点的 next 指针跳过紧挨着的相同值的结点，指向后面一个结点。这样遍历下来，所有重复的结点都会被跳过，留下的链表就是没有重复项的了。 关键点解析 代码 解法一： class Solution { public: ListNode* deleteDuplicates(ListNode* head) { Lis....

题目地址 https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/ 题目描述 Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Example 1: Input: 1->2->3->3->4->4->5 Output: 1->2->5 Example 2: Input: 1->1->1->2->3 Output: 2->3 思路 和之前那道 Remove Duplicates from Sorted List 不同的地方是这里要删掉所有的重复项，由于链表开头可能会有重复项，被删掉的话头指针会改变，而最终却还需要返回链表的头指针。所以需要定义一个新的节点，然后链上原链表，然后定义一个前驱指针和一个现指针，每当前驱指针指向新建的....