diff --git a/Week_01/id_15/LeetCode_20_isValid_15.java b/Week_01/id_15/LeetCode_20_isValid_15.java
new file mode 100644
index 00000000..9296ba4e
--- /dev/null
+++ b/Week_01/id_15/LeetCode_20_isValid_15.java
@@ -0,0 +1,29 @@
+package com.haotone.week_01;
+
+import java.util.Stack;
+
+class Solution {
+    public boolean isValid(String s) {
+        
+        if(s == null || "".equals(s)) return true;
+        char[] charArray = s.toCharArray();
+        Stack sta = new Stack();
+        for(char a:charArray){
+
+            if(sta.isEmpty()){
+                sta.push(a);
+                continue;
+            } 
+            char peek = (char)sta.peek();
+            if((peek=='(' && a==')')
+                    || (peek=='[' && a==']')
+                    || (peek=='{' && a=='}'))
+                sta.pop();
+            else 
+                sta.push(a);
+        }
+        if(sta.isEmpty()) return true;
+        else return false;
+        
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_15/LeetCode_21_mergeTwoLists_15.java b/Week_01/id_15/LeetCode_21_mergeTwoLists_15.java
new file mode 100644
index 00000000..2ee163f8
--- /dev/null
+++ b/Week_01/id_15/LeetCode_21_mergeTwoLists_15.java
@@ -0,0 +1,40 @@
+package com.haotone.week_01;
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        
+    	ListNode hummy = new ListNode(-1);
+    	ListNode cur = hummy;
+    	while(l1!=null || l2!=null){
+    		if(l1 == null){
+    			cur.next = l2;
+    			cur = l2;
+    			l2 = l2.next;
+    		}else if(l2 == null){
+    			cur.next = l1;
+    			cur = l1;
+    			l1 = l1.next;
+    		}else{
+    			if(l1.val>l2.val){
+        			cur.next = l2;
+        			cur = l2;
+        			l2 = l2.next;
+        		}else{
+        			cur.next = l1;
+        			cur = l1;
+        			l1 = l1.next;
+        		}
+    		}
+    		
+    	}
+    	return hummy.next;
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_15/LeetCode_83_deleteDuplicates_15.java b/Week_01/id_15/LeetCode_83_deleteDuplicates_15.java
new file mode 100644
index 00000000..c961eb2f
--- /dev/null
+++ b/Week_01/id_15/LeetCode_83_deleteDuplicates_15.java
@@ -0,0 +1,31 @@
+package com.haotone.week_01;
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode deleteDuplicates(ListNode head) {
+        if(head == null) return null;
+        HashSet key = new HashSet();
+        key.add(head.val);
+        ListNode node=head.next;
+        ListNode pre = head;
+        while(node!=null){
+            if(key.contains(node.val)){
+                pre.next = pre.next.next;
+            }
+            else{
+                key.add(node.val);
+                pre = node;
+            } 
+             node = node.next;
+        }
+        return head;
+        
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_15/LeetCode_905_sortArrayByParity_15.java b/Week_01/id_15/LeetCode_905_sortArrayByParity_15.java
new file mode 100644
index 00000000..10fa304f
--- /dev/null
+++ b/Week_01/id_15/LeetCode_905_sortArrayByParity_15.java
@@ -0,0 +1,27 @@
+package com.haotone.week_01;
+
+class Solution {
+    public int[] sortArrayByParity(int[] A) {
+        int befor = 0;
+		int after = A.length-1;
+		while(befor<after){
+			
+			if(A[befor]%2 != 0 && A[after]%2 == 0){
+				int temp = A[befor];
+				A[befor] = A[after];
+				A[after] = temp;
+				befor++;
+				after--;
+			}
+			if(A[befor]%2 == 0){
+				befor++;
+			}
+			if(A[after]%2 != 0){
+				after--;
+			}
+			
+		}
+        return A;
+        
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_15/LeetCode_922_sortArrayByParityII_15.java b/Week_01/id_15/LeetCode_922_sortArrayByParityII_15.java
new file mode 100644
index 00000000..692d8f91
--- /dev/null
+++ b/Week_01/id_15/LeetCode_922_sortArrayByParityII_15.java
@@ -0,0 +1,27 @@
+package com.haotone.week_01;
+
+class Solution {
+    public int[] sortArrayByParityII(int[] A) {
+        
+        int ou = 0;
+		int ji = 1;
+		int n = A.length;
+		while(ji<=n-1 && ou<=n-2){
+			
+			
+			if(A[ji]%2!=0){
+				ji += 2;
+			}else if(A[ou]%2==0){
+				ou += 2;
+			}else if(A[ji]%2==0 && A[ou]%2!=0){
+				int temp = A[ji];
+				A[ji] = A[ou];
+				A[ou] = temp;
+				ji += 2;
+				ou += 2;
+			}
+		}
+		return A;
+        
+    }
+}
\ No newline at end of file
diff --git a/Week_02/id_15/LeetCode_242_isAnagram_15.java b/Week_02/id_15/LeetCode_242_isAnagram_15.java
new file mode 100644
index 00000000..20fc4658
--- /dev/null
+++ b/Week_02/id_15/LeetCode_242_isAnagram_15.java
@@ -0,0 +1,28 @@
+package com.haotone.week_01;
+
+import java.util.HashMap;
+
+class Solution {
+    public boolean isAnagram(String s, String t) {
+        char[] sarr = s.toCharArray();
+		char[] tarr = t.toCharArray();
+		HashMap<Character,Integer> dic = new HashMap<Character,Integer>();
+		if(sarr.length != tarr.length) return false;
+		for(int i=0;i<sarr.length;i++){
+			char c = sarr[i];
+			if(dic.containsKey(c)) dic.put(c, dic.get(c)+1);
+			else dic.put(c, 1);
+		}
+		for(int i=0;i<tarr.length;i++){
+			char c = tarr[i];
+			if(dic.containsKey(c)){
+				dic.put(c, dic.get(c)-1);
+				if(dic.get(c)==0) dic.remove(c);
+			} 
+			else return false;
+		}
+		if(dic.size()>0) return false;
+		return true;
+        
+    }
+}
\ No newline at end of file
diff --git a/Week_02/id_15/LeetCode_783_minDiffInBST_15.java b/Week_02/id_15/LeetCode_783_minDiffInBST_15.java
new file mode 100644
index 00000000..56e89911
--- /dev/null
+++ b/Week_02/id_15/LeetCode_783_minDiffInBST_15.java
@@ -0,0 +1,54 @@
+package com.haotone.week_01;
+
+import java.util.HashMap;
+
+/**
+ * Definition for a binary tree node.
+ *  */
+class TreeNode {
+     int val;
+     TreeNode left;
+     TreeNode right;
+     TreeNode(int x) { val = x; }
+ }
+
+class Solution {
+    public int minDiffInBST(TreeNode root) {
+    	if(root == null) return Integer.MAX_VALUE;
+    	if(root.left == null&&root.right == null) return Integer.MAX_VALUE;
+    	if(root.left == null){
+    		int ri = root.right.val-root.val;
+    		int rimin = minDiffInBST(root.right);
+    		int rile = Integer.MAX_VALUE;
+    		if(root.right.left != null) {
+        		rile = root.right.left.val-root.val;
+        	}
+    		return Math.min(Math.min(ri, rimin),rile);
+    	}else if(root.right == null){
+    		int le = root.val-root.left.val;
+    		int lemin = minDiffInBST(root.left);
+    		int leri = Integer.MAX_VALUE;
+    		if(root.left.right != null) {
+        		leri = root.val-root.left.right.val;
+        	}
+    		return Math.min(Math.min(le, lemin),leri);
+    	} 
+    	int le = root.val-root.left.val;
+    	int ri = root.right.val-root.val;
+    	int cur = Math.min(le, ri);
+    	int rimin = minDiffInBST(root.right);
+    	int lemin = minDiffInBST(root.left);
+    	int chimin = Math.min(rimin, lemin);
+    	int leri = Integer.MAX_VALUE;
+    	int rile = Integer.MAX_VALUE;
+    	if(root.left.right != null) {
+    		leri = root.val-root.left.right.val;
+    	}
+    	if(root.right.left != null) {
+    		rile = root.right.left.val-root.val;
+    	}
+    	int aromin = Math.min(rile, leri);
+    	return Math.min(Math.min(chimin,aromin),cur);
+        
+    }
+}
\ No newline at end of file