logseq_notes/journals/2023_03_28.md

• Daily reflection Daily reflections collapsed:: true
  • What I've done
  • What I've thought #thoughts
    • 10:08
      • logseq 比 obsidian 好用，计笔记成本低，而且好用，便携。
  • Mood
    • 10:09
      • 平静且开心(lol)
• DONE [#C] 票在书包里 SCHEDULED: <2023-03-30 Thu>
• Todos:
  • Personal
    • DONE 重新浸洗袜子和内裤 SCHEDULED: <2023-03-28 Tue 13:00> :LOGBOOK: CLOCK: [2023-03-28 Tue 15:55:30]--[2023-03-28 Tue 15:55:31] => 00:00:01 :END:
    • DONE 洗眼镜 SCHEDULED: <2023-03-28 Tue 13:00> :LOGBOOK: CLOCK: [2023-03-28 Tue 18:07:51]--[2023-03-28 Tue 22:41:19] => 04:33:28 :END:
    • DONE Anki card for cloud collection 还不如没事多翻下书 SCHEDULED: <2023-04-01 Sat>
  • School
    • DONE 交选题 :LOGBOOK: CLOCK: [2023-03-28 Tue 16:19:35] CLOCK: [2023-03-28 Tue 16:19:40]--[2023-03-28 Tue 18:51:31] => 02:31:51 :END:
    • DONE [#A] 复习 java :LOGBOOK: CLOCK: [2023-03-28 Tue 20:03:20]--[2023-03-29 Wed 22:25:48] => 26:22:28 :END:
      • DONE 做题 :LOGBOOK: CLOCK: [2023-03-28 Tue 20:03:29]--[2023-03-29 Wed 11:11:16] => 15:07:47 :END:
        • DONE 练习题 :LOGBOOK: CLOCK: [2023-03-28 Tue 20:03:51]--[2023-03-28 Tue 20:39:32] => 00:35:41 :END:
        • DONE 往年题 :LOGBOOK: CLOCK: [2023-03-28 Tue 20:03:50]--[2023-03-28 Tue 22:41:14] => 02:37:24 :END:
        • DONE Leetcode :LOGBOOK: CLOCK: [2023-03-29 Wed 11:19:02] CLOCK: [2023-03-29 Wed 11:19:04]--[2023-03-29 Wed 16:52:09] => 05:33:05 :END:
      • DONE 看 ppt :LOGBOOK: CLOCK: [2023-03-28 Tue 20:03:30]--[2023-03-29 Wed 11:18:53] => 15:15:23 :END:
• OJ problem notes
  • Name:
    • Contains Duplicate
  • Times:
    • Completion time: 14:31
    • Revisions:
  • Tags:
    • Data structures: #hash_table
    • Difficulty: #difficulty_easy
    • Platforms: #leetcode
  • Links:
    • link to the problem
  • Problem:
    • Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.
  • Examples:

    • 
      
      Example 1:
      
      Input: nums = [1,2,3,1]
      Output: true
      
      Example 2:
      
      Input: nums = [1,2,3,4]
      Output: false
      
      Example 3:
      
      Input: nums = [1,1,1,3,3,4,3,2,4,2]
      Output: true
      
      

  • Constraints:
    • 1 <= nums.length <= 105
    • -109 <= nums[i] <= 109
  • Thoughts:
    • Very simple hash map problem
  • Solution:

    • class Solution {
          public boolean containsDuplicate(int[] nums) {
              Set <Integer> set = new HashSet<Integer>();
              for (int i : nums) {
                  if (set.contains(i)) {
                      return true;
                  } else {
                      set.add(i);
                  }
              }
      
              return false;
          }
      }
      
• Java 练习题 1 #to_be_deleted collapsed:: true
  • Q1
    • less than 10
  • Q2
    • greater than 10
  • Q3
    • yes
  • Q4

    • zero
      one
      none
      

  • Q5

    • zero
      one
      none
      one
      none
      none
      

  • Q6

    • zero
      none
      one
      zero
      none
      none
      

  • Q7

    • int sum;
      for (int i = 1; i <= 100; i++) {
        sum += i;
      }
      System.out.println(sum);
      

  • Q8

    • for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 3; j++) {
          System.out.print(i * j + " ");
        }
        System.out.println();
      }
      

  • Q9

    • 9
      8
      true
      

  • Q10

    • int sum = 0;
      for (int i = 1; i <= 99; i++) {
        if (i % 3 == 0) {
          sum += i;
        }
      }
      System.out.println(sum);
      

  • Q11 不想写
  • Q12
    • What does overloading mean?
    • What does overloading do?
• java 练习题 2 qmplus #to_be_deleted
  • Q1
    • no.1 : not a array no.2 : int[] marks = new int[60] no.3 : {'a', 'b', 'c'} no.4 : use ""
  • Q2
    • Compile error
  • Q3
    • F[1] is not initiated, it only has a null value
  • Q4
    • Array index out of bounds, f[2] is non-exist
  • Q5
    • compile error, local variable won't be initialized as default val
  • Q6
    • 36, 36.0
  • Q7
    • first one invalid
      • Reason: wrong parameters
    • third one invalid
      • Reason: double->int can't be done implicitly, you have to use type casts
  • Q8

    • vroom
      truck 1
      car 2
      

  • Q9

    • vroomT
      truck 1
      car 1
      

  • Q10
    • 634.5
    • Reason: calculated from left to right, all converted to String
  • Q11
    • F, only have access to package-private data
    • F, no multi-inheritance for classes
    • F, not required
    • F, you can have one
  • Q12
    • b
  • Q13
    • false
    • true
    • true (reference stored in string constant pool)
  • Q14 collapsed:: true
    • 懒得写了
  • Q15 collapsed:: true
    • 懒得写
  • Q16
    • What is a abstract class?
    • What is toString method?
    • What does polymorphism mean?