[Function add]

1. Add leetcode solutions.

Author: Botao Xiao

README.md

@@ -309,6 +309,10 @@
 
 [172. Factorial Trailing Zeroes](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/172.%20Factorial%20Trailing%20Zeroes.md)
 
+[173. Binary Search Tree Iterator](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/173.%20Binary%20Search%20Tree%20Iterator.md)
+
+[175. Combine Two Tables](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/175.%20Combine%20Two%20Tables.md)
+
 ## Algorithm(4th_Edition)
 Reading notes of book Algorithm(4th Algorithm),ISBN: 9787115293800.
 All java realization codes are placed in different packages.

leetcode/173. Binary Search Tree Iterator.md

@@ -102,4 +102,44 @@ public class BSTIterator {
  * BSTIterator i = new BSTIterator(root);
  * while (i.hasNext()) v[f()] = i.next();
  */
-```
+```
+
+### 二刷
+```Java
+/**
+ * Definition for binary tree
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class BSTIterator {
+    private List<Integer> inorder = new LinkedList<>();
+    private ListIterator<Integer> cur = null;
+    public BSTIterator(TreeNode root) {
+        inorder(root, inorder);
+        cur = inorder.listIterator(0);
+    }
+    private void inorder(TreeNode root, List<Integer> list){
+        if(root == null) return;
+        inorder(root.left, list);
+        list.add(root.val);
+        inorder(root.right, list);
+    }
+    /** @return whether we have a next smallest number */
+    public boolean hasNext() {
+        return cur.hasNext();
+    }
+    /** @return the next smallest number */
+    public int next() {
+        return cur.next();
+    }
+}
+/**
+ * Your BSTIterator will be called like this:
+ * BSTIterator i = new BSTIterator(root);
+ * while (i.hasNext()) v[f()] = i.next();
+ */
+```

leetcode/175. Combine Two Tables.md

@@ -42,4 +42,17 @@ left join
     Address
 on
     Person.PersonId = Address.PersonId;		//以id作为连接点。
-```
+```
+
+### 二刷
+1. 我们应该使用左外连接。
+2. 我们使用Person作为左表，以左表为基准，获得所有的信息。
+```Java
+# Write your MySQL query statement below
+SELECT
+    p.FirstName, p.LastName, a.City, a.State
+FROM Person p
+LEFT OUTER JOIN
+Address a
+ON p.PersonId = a.PersonId;
+```