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--- java_primer [2020/08/18 16:02] – jrseti
+++ java_primer [2020/11/19 17:19] (current) – [LinkedHashMap] jrseti
@@ Line 17: / Line 17: @@
   * But, **keys are ordered**!
   * No null keys
+  * keySet()and values() return in ascending order
 ====LinkedHashMap====
+**An OrderedDict!**
 Same as hashMap but preserves **insertion order**. O(1) insertion and lookup.
@@ Line 28: / Line 31: @@
 map.getOrDefault(key, default_value);
+====HashSet====
+<code>
+HashSet<String> h = new HashSet<String>();
+h.add"(a");
+h.add("b");
+Iterator<String> i = h.iterator();
+while (i.hasNext()) {
+   System.out.println(i.next());
+}</code>
+contains(), add(), isEmpty(), size(), clone()
 ====Map Iteration=====
@@ Line 89: / Line 105: @@
      }
 </code>
+=====Stacks=====
+<code>import java.util.*
+Stack<Integer> stack = new Stack<>();;
+</code>
+pop(), peek(), push(), empty(), search()
+=====Queue=====
+<code>
+import java.util.LinkedList;
+import java.util.Queue;
+Queue<Integer> q = new LinkedList<>();
+</code>
+=====PriorityQueue=====
+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=====
+====Traversing====
+<code>
+TreeNode cur = root;
+int min = Integer.MAX_VALUE;
+int max = Integer.MIN_VALUE;
+while(cur != null ||
+</code>
+=====NOTES=====
+  * Vector is the same as ArrayList, but Vector is synchronized. Removing from Vector or ArrayList in O(n).
+  * LinkedList has O(1) remove, LinkedList is a double linked list. ArrayList is single.
+  * LinkedList is better with add(), remove.
+  * 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>