xin_rong的博客

Recursive:Java:private List<List<Integer>> dfs(Node node, List<List<Integer>> res, int level) { if (node == null) return res; if (res.size() == level) res.add(new ArrayList<>()); res.get(level).a..

Recursive:Java:class Solution { public List<Integer> list = new ArrayList<>(); public List<Integer> preorder(Node root) { if (root == null) return list; list.add(root.val); for(N..

Recursive:Java:class Solution { List<Integer> list = new ArrayList<>(); public List<Integer> postorder(Node root) { if (root == null) return list; for(Node node: root.children) ..

Recursive:Java:public List<Integer> preorderTraversal(TreeNode root) { List<Integer> pre = new LinkedList<Integer>(); preHelper(root,pre); return pre;}public void preHelper(TreeNode root, List<Integer> pre) { if(root==nul

Iterativeright child doesn't exist: save all the children on the left chain does exist: save the top of the stack in the resultPython:def inorderTraversal(self, root): res, stack = [], [] while (root or stack...

Given an array of stringsstrs, groupthe anagramstogether. You can return the answer inany order.AnAnagramis a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once....

Solutions:(1) Arrays.sort(str) directlyJava:public boolean isAnagram(String s, String t) { if (s.length() != t.length()) { return false; } char[] str1 = s.toCharArray(); char[] str2 = t.toCharArray(); Arrays.sort(str1);..

You are given an array of integersnums, there is a sliding window of sizekwhich is moving from the very left of the array to the very right. You can only see theknumbers in the window. Each time the sliding window moves right by one position.Return...

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) -- Push element x onto stack. pop() -- Removes the element on top of the stack. top() -- Get the top element. getMin() -- Retrieve the minimum ele

Given a stringscontaining just the characters'(',')','{','}','['and']', determine if the input string is valid.An input string is valid if:Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct ...

Givennnon-negative integers representing an elevation map where the width of each bar is1, compute how much water it can trap after raining.Solutions:ans = sum {min⁡(left_max,right_max)−height[i]min(left_max,right_max)−height[i] for all element...

Solutions:C++:#include <vector>#include <iostream>using namespace std;class MyCircularDeque {private: vector<int> buffer; int cnt; int k; int front; int rear;public: /** Initialize your data structure..

Given anon-emptyarray of decimal digitsrepresenting a non-negative integer, incrementone to the integer.The digits are stored such that the most significant digit is at the head of the list, and each element in the array contains a single digit.You...

Given two sorted integer arraysnums1andnums2, mergenums2intonums1as one sorted array.Note:The number of elements initialized innums1andnums2aremandnrespectively. You may assume thatnums1has enough space (size that isequaltom+n) t...

Givennnon-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.

Merge two sorted linked lists and return it as a newsortedlist. The new list should be made by splicing together the nodes of the first two lists.Solutions:(1) Recursive:The recursive function mergeTwoLists(ListNode l1, ListNode l2) mean merge...

Given an array, rotate the array to the right byksteps, wherekis non-negative.Follow up:Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem. Could you do it in-place with O(1) extra space?So...

Given a linked list, reverse the nodes of a linked listkat a time and return its modified list.kis a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple ofkthen left-out nodes, in the...

Given a sorted arraynums, remove the duplicatesin-placesuch that each element appears onlyonceand returns the new length.Do not allocate extra space for another array, you must do this bymodifying the input arrayin-placewith O(1) extra memory.C...

Given a linked list, return the node where the cycle begins. If there is no cycle, returnnull.There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following thenextpointer. Internally,posis us...

Givenhead, the head of a linked list, determine if the linked list has a cycle in it.There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following thenextpointer. Internally,posis used to den...

Given alinked list, swap every two adjacent nodes and return its head.You maynotmodify the values in the list's nodes. Only nodes itself may be changed.Solutions:(1) Recursive: when head.next.next pairs are swapped, only need to swap the first t...

Reverse a singly linked list.Example:Follow up:A linked list can be reversed either iteratively or recursively. Could you implement both?Solutions:(1) IterativeWe want the curr->next to be prev and in order to iterate in the loop, three.

You are climbing a staircase. It takes n steps to reach the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?Solutions:(1) Appliesto a small nTry to compose the big abstract problem by simila..

Given n non-negative integers a1, a2, ..., an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of the line i is at (i, ai) and (i, 0). Find two lines, which, together with the x-axis forms a cont.

Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements.Solutions:(1) In the first loop, count the number of zeros. In the second loop, if not zero, move forward; ...

Given an arraynumsofnintegers, are there elementsa,b,cinnumssuch thata+b+c= 0? Find all unique triplets in the array which gives the sum of zero.Notice that the solution set must not contain duplicate triplets.Solutions:(1) O(n^3...

1. Two SumGiven an array of integersnumsand an integertarget, returnindices of the two numbers such that they add up totarget.You may assume that each input would haveexactlyone solution, and you may not use thesameelement twice.You can retu...

解析：每种方法都需要设置代表首、尾的变量，设为front、rear。 在rear位置插入即入队列，front位置删除即出队列。 循环队列找到首尾的算法都是 (rear或front + 1) % length。C++class MyCircularQueue {public: /** Initialize your data structure here. Set th...