JAVA - OOP - PASS BY VALUE / PASS BY REFERENCE

  Always consider to new a object to copy , and aware you are using reference of value! 


Always remember pass by value or pass by reference
eg.

List<List<sth>>
Array





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MAP - Sort with stream

 LEETCODE 1636 Given an array of integers   nums , sort the array in   increasing   order based on the frequency of the values. If multiple values have the same frequency, sort them in   decreasing   order. Return the  sorted array . Example 1: Input: nums = [1,1,2,2,2,3] Output: [3,1,1,2,2,2] Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and '2' has a frequency of 3. Example 2: Input: nums = [2,3,1,3,2] Output: [1,3,3,2,2] Explanation: '2' and '3' both have a frequency of 2, so they are sorted in decreasing order. Example 3: Input: nums = [-1,1,-6,4,5,-6,1,4,1] Output: [5,-1,4,4,-6,-6,1,1,1] #1 class Solution { public int[] frequencySort(int[] nums) { return Arrays.stream(nums) .boxed() // boxing to wapped class .collect(Collectors.toMap(e-> e , e-> 1 , Integer::sum))//?? .entrySet() .stream() .sorted((e1,e2) -> e1.getValue().equals(e...
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JAVA - DSF Example

  class Solution { class Point { int x ; int y ; int steps ; public Point ( int x , int y , int steps ){ this . x = x; this . y = y; this . steps = steps; } } public int shortestPathBinaryMatrix ( int [][] grid ) { //BFS //DFS //BFS -> Shortest path //DSA : Queue if (grid[ 0 ][ 0 ] != 0 ){ return - 1 ; } int [][] moves = new int [][]{{ 0 ,- 1 } , { 0 , 1 } , { 1 , 0 }, {- 1 , 0 } , {- 1 ,- 1 },{- 1 , 1 },{ 1 , 1 },{ 1 ,- 1 }}; Stack < Point > queue = new Stack <>(); queue . push ( new Point ( 0 , 0 , 1 )); grid[ 0 ][ 0 ] = 1 ; int newX = 0 ; int newY = 0 ; while (! queue . isEmpty ()){ Point point = queue . pop (); if ( point . x == grid . length - 1 && point . y == grid[ 0 ]. length - 1 ){ ...
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