刷题记录帖

637. Average of Levels in Binary Tree

https://www.geeksforgeeks.org/linked-list-set-1-introduction/
Design of linked list.
426. Convert Binary Search Tree to Sorted Doubly Linked List17. Letter Combinations of a Phone Number
刷题列表
https://www.educative.io/courses ... d=5749180081373184/

637. Average of Levels in Binary Tree

https://www.geeksforgeeks.org/linked-list-set-1-introduction/
Design of linked list.
426. Convert Binary Search Tree to Sorted Doubly Linked List
刷题列表
https://www.educative.io/courses ... d=5749180081373184/

Methods in Java
https://www.geeksforgeeks.org/methods-in-java/
StringBuffer class in Java
https://www.geeksforgeeks.org/stringbuffer-class-in-java/
StringBuilder Class in Java with Examples
https://www.geeksforgeeks.org/st ... java-with-examples/

Main thread in Java
https://www.geeksforgeeks.org/main-thread-java/
Synchronized in Java
https://www.geeksforgeeks.org/synchronized-in-java/


17. Letter Combinations of a Phone Number
done! hao ti
what I learn from this problem?
how to convert charArray to string?
String s = new String(charArray);
String[] map = {" ","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
int index = digits.charAt(i)-'0';

how to do it in iterative way?
46. Permutations
77. Combinations

/*Given 2-d array filled with numbers, try to get max block area with same value which constructed only by
// horizontal or vertical lines, example


// 11234
// 23102
// 23015
// Would return 2,

// 111234
// 010234
// Return 4

// 111111
// 111101
// 111111
// 111111
// Return 23
// */

/*
*[
[1, -2, 3, 4],
[-2, 2, 3, 1],
[1, 3, -1, 1]
]
*/

周六

200. Number of Islands
490. The Maze
https://www.geeksforgeeks.org/iterators-in-java/

200. Number of Islands

done
dfs and bfs

there is a bug here.

108. Convert Sorted Array to Binary Search Tree

490. The Maze
https://www.geeksforgeeks.org/iterators-in-java/


17. Letter Combinations of a Phone Number
104. Maximum Depth of Binary Tree

257. Binary Tree Paths
https://www.geeksforgeeks.org/lambda-expressions-java-8/


Study udemy SDET.
Learn about thread.
pattern design: singleton design, factory pattern design.
write a code and write test cases for it.

retrospective. and prepare the interview

implementatuon of queue
622. Design Circular Queue
933. Number of Recent Calls
346. Moving Average from Data Stream
621. Task Scheduler

286. Walls and Gates

286. Walls and Gates
write down another idea.
learn to write with directions.
study why there is out of bound error.
200. Number of Islands
learn to write using directions.
study why there is out of bound error.
752. Open the Lock
int y = ((node.charAt(i) - '0') + d + 10) % 10;
                        String nei = node.substring(0, i) + ("" + y)(why) + node.substring(i+1);

public static int openLock(String[] deadends, String target) {
        Queue<String> q = new LinkedList<>();
        Set<String> visited = new HashSet<>(Arrays.asList(deadends));

List addAll() Method in Java with Examples
q.addAll(getSuccessors(node));
private static List<String> getSuccessors(String str) {
        List<String> res = new LinkedList<>();
        for (int i = 0; i < str.length(); i++) {
            res.add(str.substring(0, i) + (str.charAt(i) == '0' ? 9 :  str.charAt(i) - '0' - 1) + str.substring(i+1));
            res.add(str.substring(0, i) + (str.charAt(i) == '9' ? 0 :  str.charAt(i) - '0' + 1) + str.substring(i+1));
        }
        return res;
    }
Syntax:

boolean addAll(Collection c)
Parameters: This function has a single parameter, i.e, Collection c, whose elements are to be appended to the list.

practice tmr
https://leetcode.com/problems/op ... 2B-how-to-avoid-TLE

127. Word Ladder
Good!
https://leetcode.com/problems/wo ... pted-Java-solution-(BFS)


279. Perfect Squares
study tmr

Valid Parentheses
recursion

735. Asteroid Collision
394. Decode String
Daily Temperatures
150. Evaluate Reverse Polish Notation
string manipulation
convert a string to integer
how to convert a character to integer?
how to compare two string

mock interview.
finish matrix one
learn DP.

number manipulation

202.Happy Number
43. Multiply Strings
7. Reverse Integer
9. Palindrome Number


two pointer technique
141. Linked List Cycle
202.Happy Number
method calling
run test case


how to nama a variable?
what is the naming rule?


13. Roman to Integer
hashmap/switch


ArrayList:
347. Top K Frequent Elements
bucket sort