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java_primer

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java_primer [2020/08/18 16:32] – [HashSet] jrsetijava_primer [2020/11/19 17:19] (current) – [LinkedHashMap] jrseti
Line 17: Line 17:
   * But, **keys are ordered**!   * But, **keys are ordered**!
   * No null keys   * No null keys
 +  * keySet()and values() return in ascending order
  
 ====LinkedHashMap==== ====LinkedHashMap====
 +
 +**An OrderedDict!**
  
 Same as hashMap but preserves **insertion order**. O(1) insertion and lookup. Same as hashMap but preserves **insertion order**. O(1) insertion and lookup.
Line 105: Line 108:
 =====Stacks===== =====Stacks=====
  
-<code>import java.util.*</code>+<code>import java.util.* 
 +Stack<Integer> stack = new Stack<>();; 
 +</code>
  
 pop(), peek(), push(), empty(), search() pop(), peek(), push(), empty(), search()
Line 121: Line 126:
 https://www.geeksforgeeks.org/priority-queue-class-in-java-2/ https://www.geeksforgeeks.org/priority-queue-class-in-java-2/
  
 +poll(), remove(), add()
  
 +
 +
 +<code>
 +class The_Comparator implements Comparator<String> { 
 +    public int compare(String str1, String str2) 
 +    { 
 +        String first_Str; 
 +        String second_Str; 
 +        first_Str = str1; 
 +        second_Str = str2; 
 +        return second_Str.compareTo(first_Str); 
 +    } 
 +} 
 +
 +PriorityQueue<String> queue = new PriorityQueue<String>(new The_Comparator()); 
 +        
 +</code>
 =====DFS===== =====DFS=====
  
Line 141: Line 164:
   * LinkedList is better with add(), remove.    * LinkedList is better with add(), remove. 
   * ArrayList better with get(), set().   * ArrayList better with get(), set().
 +
 +  * Char to digit: s.charAt(num2Idx) - '0'
 +
 +
 +=====TRICKS=====
 +
 +====Log and division====
 +
 +  * a / b = Math.exp(Math.log(a) - Math.log(b))
 +
 +====Random====
 +
 +<code>
 +//Random number from 0 to 5
 +Random rand = new Random(); 
 +int r = rand.nextInt(6); 
 +</code>
 +
 +or
 +
 +<code>
 +//Number between 0.0 and 1.0;
 +Math.random(); 
 +</code>
  
java_primer.1597768372.txt.gz · Last modified: 2020/08/18 16:32 by jrseti