[Function add]

1.SunProblems.
2.Use list to realize a bag frame.

Author: Seanforfun

Algorithm(4th_Edition)/algorithm_note.txt

@@ -91,6 +91,8 @@
 		1.a在堆上开辟了一块空间，用于存储2018-1-1.
 		2.b在堆上开辟了一块空间，用于存储2018-3-13.
 		3.a指向b所对应的空间，此时2018-1-1对应的空间则没有任何的引用成为孤儿对象，则会被JVM的垃圾回收机制(Garbage Collection,GC)回收。
+			->垃圾回收的时间是难以预估的。
+			->没有引用的对象（或者说没有办法访问到的对象），被JVM视为孤儿对象，将会被GC回收。
 
 9. 背包***：
 	接口：ca.mcmaster.chapter.one.bag.Bag<T>
@@ -102,6 +104,40 @@
 		Integer size();
 	}
 
+	->链表实现背包：
+	实现：ca.mcmaster.chapter.one.bag.ListBag<T>
+	public class ListBag<T> implements Bag<T>{
+		private Node first;
+		private Integer size = 0;
+		private class Node{
+			T t;
+			Node next;
+		}
+		public void add(T t) {
+			Node oldFirst  = first;
+			first = new Node();
+			first.t = t;
+			first.next = oldFirst;
+			size++;
+		}
+		public Boolean isEmpty() { return size.equals(0); };
+		public Integer size() { return size; }
+		public Iterator<T> iterator() {
+			return new ListIterator();
+		}
+		private class ListIterator implements Iterator<T>{
+			private Node current = first;
+			public boolean hasNext() { return current != null; }
+			public T next() {
+				if(!hasNext()) throw new IndexOutOfBoundsException();
+				T t = current.t;
+				current = current.next;
+				return t;
+			}
+			public void remove() {}
+		}				
+	}
+	
 10. FIFO队列：
 	接口：ca.mcmaster.chapter.one.FIFO.FifoQueue<T>
 	public interface FifoQueue<T> extends Iterable<T> {
@@ -259,4 +295,23 @@
 			System.out.println(value.pop());
 		}
 	}
+	
+14.	算法分析：
+	增长数量级函数（大到小）
+	指数级别 > 立方级别 > 平方级别 || > 线性对数（NlogN）> 线性级别 > || 对数级别 > 常数级别
+	
+15. Sum问题：
+	给定一组不同数组，找其中为和为0的组合的个数：
+	->TwoSum:
+	1.BrutalTwoSum:O(N^2)
+	2.FastTwoSum:O(NlogN)
+		实现：ca.mcmaster.chapter.one.sum.SumProblems#twoSumFast(Integer[])
+		1.对数组进行排序。
+		2.对于所有元素进行遍历O(N)
+		3.通过二分法寻找相反数，如果相反数对应的位置大于当前的index则说明一对TwoSum存在。
+	->ThreeSum:
+		实现：ca.mcmaster.chapter.one.sum.SumProblems#threeSumFast(Integer[])
+		1.对数组进行排序。
+		2.对数组进行二维遍历O(N^2)。
+		3.通过二分法寻找a[i]+a[j]相反数，如果相反数对应的位置大于当前的index则说明一对ThreeSum存在。
 

…c/ca/mcmaster/chapter/one/Recursive.java …a/mcmaster/chapter/one/BinarySearch.javaAlgorithm(4th_Edition)/src/ca/mcmaster/chapter/one/Recursive.java renamed to Algorithm(4th_Edition)/src/ca/mcmaster/chapter/one/BinarySearch.java Algorithm(4th_Edition)/src/ca/mcmaster/chapter/one/Recursive.java renamed to Algorithm(4th_Edition)/src/ca/mcmaster/chapter/one/BinarySearch.java

@@ -1,6 +1,6 @@
 package ca.mcmaster.chapter.one;
 
-public class Recursive {
+public class BinarySearch {
 	private static int rank(int key, int[] a){
 		return rank(key, a, 0, a.length - 1);
 	}

Algorithm(4th_Edition)/src/ca/mcmaster/chapter/one/bag/ListBag.java

@@ -0,0 +1,46 @@
+package ca.mcmaster.chapter.one.bag;
+
+import java.util.Iterator;
+
+public class ListBag<T> implements Bag<T>{
+	private Node first;
+	private Integer size = 0;
+	private class Node{
+		T t;
+		Node next;
+	}
+	public void add(T t) {
+		Node oldFirst  = first;
+		first = new Node();
+		first.t = t;
+		first.next = oldFirst;
+		size++;
+	}
+	public Boolean isEmpty() { return size.equals(0); };
+	public Integer size() { return size; }
+	public Iterator<T> iterator() {
+		return new ListIterator();
+	}
+	private class ListIterator implements Iterator<T>{
+		private Node current = first;
+		public boolean hasNext() { return current != null; }
+		public T next() {
+			if(!hasNext()) throw new IndexOutOfBoundsException();
+			T t = current.t;
+			current = current.next;
+			return t;
+		}
+		public void remove() {}
+	}
+	
+	public static void main(String[] args) {
+		ListBag<Integer> bag = new ListBag<>();
+		for(int i = 0; i < 10; i++){
+			bag.add(i);
+		}
+		Iterator<Integer> it = bag.iterator();
+		while (it.hasNext()) {
+			System.out.println(it.next());
+		}
+	}
+}

Algorithm(4th_Edition)/src/ca/mcmaster/chapter/one/sum/SumProblems.java

@@ -0,0 +1,36 @@
+package ca.mcmaster.chapter.one.sum;
+
+import java.util.Arrays;
+
+public class SumProblems {
+	public static int twoSumFast(Integer[] a){
+		Arrays.sort(a);
+		Integer length = a.length;
+		int cnt = 0;
+		for(int i = 0; i < length; i++){
+			if(Arrays.binarySearch(a, -a[i]) > i){
+				cnt++;				
+			}
+		}
+		return cnt;
+	}
+	
+	public static int threeSumFast(Integer[] a){
+		int cnt = 0;
+		Arrays.sort(a);
+		Integer n = a.length;
+		for(int i = 0; i < n; i++){
+			for (int j = i+1; j < n; j++) {
+				if(Arrays.binarySearch(a, -a[i]-a[j]) > j){
+					cnt++;
+				}
+			}
+		}
+		return cnt;
+	}
+	
+	public static void main(String[] args) {
+		Integer[] a = new Integer[]{-3,2,4,-2,5,-2,-2};
+		System.out.println(threeSumFast(a));
+	}
+}