Life-coding

Solve one problem everyday.

All of my daily problem solving lives in this repo. Some of the wrong attempt is also here. If you follow this repo, make sure you run the code and try with test cases.

Amazon Leadership interview details

https://interviewgenie.com/blog-1/category/Amazon+interviews

Resources

Helper materials:

Tree:

Segment Tree: https://www.youtube.com/watch?v=Oq2E2yGadnU
AVL Tree: https://www.youtube.com/watch?v=-9sHvAnLN_w

Dynamic Programming

Understanding Longest common subsequence: https://www.youtube.com/watch?v=43P0xZp3FU4
https://avikdas.com/2019/04/15/a-graphical-introduction-to-dynamic-programming.html
Great example of dynamic programming in realworld: https://avikdas.com/2019/05/14/real-world-dynamic-programming-seam-carving.html

Understanding SSTable

* https://www.igvita.com/2012/02/06/sstable-and-log-structured-storage-leveldb/
* https://hackernoon.com/fundamentals-of-system-design-part-3-8da61773a631

Java Code Beauty:

Composition Function: http://www.deadcoderising.com/2015-09-07-java-8-functional-composition-using-compose-and-andthen/

Quick Notes

Counting character frequency in a string.

String s="HelloWorld";
Map<Character, Long> map = t.chars() //converting int stream
                  .mapToObj(c -> (char) c)//int stream to character stream
                  .collect(Collectors.groupingBy(Function.identity(),// collect by group
                          Collectors.counting()));
          System.out.println(map);

Best way to find mid point.

M=start+(end-start)/2;//overflow error free

Sort an int array in descending order

int[] sorted = IntStream.of(inputArray)
        .boxed()
        .sorted(Comparator.reverseOrder())
        .mapToInt(i -> i)
        .toArray();

Iterating over map

map.entrySet().stream().forEach(entry->{
          System.out.println("Key: "+entry.getKey()+"value: "+entry.getValue());
      });

String counting in java 8

        String[] strings=new String[]{"hello","world","hello"};
        List<String> list=Arrays.asList(strings);
        Map<String, Long> map1=         list.stream().collect(groupingBy(identity(), counting()));

Alternatively,

HashMap<String,Long> map= (HashMap<String, Long>) Arrays.stream(arr).collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));

Sort list of object based on property

 private static class Inerval {
        int start;
        int end;

        public Inerval(int start, int end) {
            this.start = start;
            this.end = end;
        }
    }
    
     ArrayList<Inerval> list=new ArrayList<>();
     list.add(new Inerval(1,3));
     list.add(new Inerval(5,8));
     list.add(new Inerval(4,10));
     list.add(new Inerval(20,25));
     list.sort(Comparator.comparingInt(v -> v.start));
     list.stream().forEach(interval -> {
                System.out.println(interval.start+"->"+interval.end);
      });

# How to sort from largest to smallest

      list.sort((i1, i2) -> {
                 if (i2.start > i1.start) return 1;//we want next bigger element first
                 else if (i1.start > i2.start) return -1;
                 else return 0;
     
             });
     
      list.stream().forEach(interval -> {
          System.out.println(interval.start + "->" + interval.end);
      });

PriorityQueue with custom comparator

 PriorityQueue<ListNode> pq = new PriorityQueue<>(Comparator.comparing(node -> node.val));

Best Way to understand backtracking

https://www.bilibili.com/video/av36351060?p=1

Best way of understanding Huffman Encoding

https://www.youtube.com/watch?v=ikswC-irwY8&list=PLnfg8b9vdpLn9exZweTJx44CII1bYczuk&index=42

Bit manipulation

x &= -x will give you the last set bit.
XOR of same two number is 0
changing a bit from 0 to 1: we can do OR operation : 0 OR 1 = 1 .

How can we change a particular bit from 0 to 1. We will do the same OR but differently. Let say input is: 1011 Take 1(4 bit binary form would be 0001) and make left shift 2 to change the third bit of input.

1<<2=0100
0100 OR 1011 = 1111

How to toggle a bit, from 0 to 1 and 1 to 0 ? we can do that by doing XOR

Now, how to toggle a particular bit, Take 1 and do left shift to find the position and do the XOR operation. Let say input is: 1011

1 << 1 = 0010
0010 XOR 1011= 1001

How to make a bit switched off? ^ Let take the input 1 0 0 1 1 1 0 1 and wants to turned off the hat bit. Take 1, do left bit shift, do NOT and finally AND operation

0 0 0 0 0 0 0 1 << 4 = 0 0 0 0 1 0 0 0
NOT(0 0 0 0 1 0 0 0) = 1 1 1 1 0 1 1 1

    1 0 0 1 1 1 0 1
AND 1 1 1 1 0 1 1 1 
------------------
    1 0 0 1 0 1 0 1

Shortcut code snippet

If you need to assign value to a variable based on comparison of others two: follow this a = b == c ? 1 : 0 means if b and c are equal assign a=1 or a=0

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