diff --git a/Week_01/id_50/LeetCode_1021_050.java b/Week_01/id_50/LeetCode_1021_050.java
new file mode 100644
index 00000000..8c8b2f81
--- /dev/null
+++ b/Week_01/id_50/LeetCode_1021_050.java
@@ -0,0 +1,62 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 删除最外层的括号
+ */
+public class LeetCode_1021_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_1021_050 solution = new LeetCode_1021_050();
+		System.out.println(solution.removeOuterParentheses("(())(()(()))"));
+	}
+
+	public String removeOuterParentheses(String S) {
+	       if(S == null){
+				return null;
+			}
+			if(S.length() == 0){
+				return "";
+			}
+			char[] charArr = S.toCharArray();
+			Stack<Character> stack = new Stack<>();
+			StringBuilder strBuild = new StringBuilder();
+			int n = 0;
+			Set<Integer> setval = new HashSet<>();
+			for(int i=0; i<charArr.length; i++){
+				if(stack.size()==0){
+					stack.add(charArr[i]);
+					setval.add(i);
+					n++;
+					continue;
+				}
+				StringBuilder strtmp = new StringBuilder();
+				if(strtmp.append(stack.get(stack.size()-1)).append(charArr[i]).toString().equals("()")){
+					if(stack.size()==1 && n==1){
+						setval.add(i);
+						n=0;
+					}
+					stack.pop();
+				}else{
+					stack.add(charArr[i]);					
+				}
+			}
+			for(int i=0; i<charArr.length; i++){
+				if(!setval.contains(i)){
+					strBuild.append(charArr[i]);
+				}
+			}
+			return strBuild.toString();
+	    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_1047_050.java b/Week_01/id_50/LeetCode_1047_050.java
new file mode 100644
index 00000000..b278a80c
--- /dev/null
+++ b/Week_01/id_50/LeetCode_1047_050.java
@@ -0,0 +1,51 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 删除字符串中的所有相邻重复项
+ */
+public class LeetCode_1047_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_1047_050 solution = new LeetCode_1047_050();
+		System.out.println(solution.removeDuplicates("abbacaacdad"));
+	}
+
+	public String removeDuplicates(String S) {
+        if(S == null){
+			return null;
+		}
+		if(S.length() == 0){
+			return "";
+		}
+		char[] charArr = S.toCharArray();
+		Stack<Character> stack = new Stack<>();
+		for(char c : charArr){
+			if(stack.size()==0){
+				stack.add(c);			
+			}else{
+				if(c == stack.get(stack.size()-1)){
+					stack.pop();
+				}else{
+					stack.add(c);
+				}
+			}
+		}
+		StringBuilder strBuild = new StringBuilder();
+		for(Character c: stack){
+			strBuild.append(c);
+		}
+		return strBuild.toString();
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_104_050.java b/Week_01/id_50/LeetCode_104_050.java
new file mode 100644
index 00000000..fba54a8a
--- /dev/null
+++ b/Week_01/id_50/LeetCode_104_050.java
@@ -0,0 +1,32 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 二叉树的最大深度
+ */
+public class LeetCode_441_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+	}
+
+	public int maxDepth(TreeNode root) {
+        if(root == null){
+			return 0;
+		}else{
+			int left = maxDepth(root.left);
+			int right = maxDepth(root.right);
+			return Math.max(left, right)+1;
+		}
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_111_050.java b/Week_01/id_50/LeetCode_111_050.java
new file mode 100644
index 00000000..bb593e2e
--- /dev/null
+++ b/Week_01/id_50/LeetCode_111_050.java
@@ -0,0 +1,43 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 二叉树的最小深度
+ */
+public class LeetCode_111_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+	}
+
+	public int minDepth(TreeNode root) {
+        if(root == null){
+			return 0;
+		}else{
+			if(root.left == null && root.right == null){
+				return 1;
+			}
+			int min_val = Integer.MAX_VALUE;
+			if(root.left != null){
+				int left = minDepth(root.left);
+				min_val = Math.min(left, min_val);
+				
+			}
+			if(root.right != null){
+				int right = minDepth(root.right);
+				min_val = Math.min(right, min_val);
+			}
+			return min_val+1;
+		}
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_189_050.java b/Week_01/id_50/LeetCode_189_050.java
new file mode 100644
index 00000000..bb465c70
--- /dev/null
+++ b/Week_01/id_50/LeetCode_189_050.java
@@ -0,0 +1,62 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ *  删除排序数组中的重复项
+ */
+public class LeetCode_189_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_189_050 solution = new LeetCode_189_050();
+		int[] nums = {1,2};
+		String[] strs = {"nozzle","punjabi","waterlogged","imprison","crux","numismatists"};
+//		System.out.println(solution.removeDuplicates(nums));
+		solution.rotate(nums, 1);	
+//		System.out.println(solution.isAnagram("dgqztusjuu", "dqugjzutss"));
+//		solution.groupAnagrams(strs);
+//		System.out.println(solution.removeDuplicates("abbacaacdad"));
+//		System.out.println(solution.removeOuterParentheses("(())(()(()))"));
+//		System.out.println(solution.arrangeCoins(2147483647));
+//		System.out.println(solution.myPow(2, 10));
+	}
+
+	public void rotate(int[] nums, int k) {
+		k = k%nums.length;
+		if( k<=0 ){
+			return;
+		}
+        int val = 0;
+        for(int i=0; i<(nums.length-k)/2; i++){
+        	val=nums[i];
+        	nums[i] = nums[nums.length-1-k-i];
+        	nums[nums.length-1-k-i] = val;
+        	
+        }
+        for(int i=nums.length-k; i<nums.length-k+k/2; i++){
+        	val=nums[i];
+        	nums[i] = nums[nums.length-1-(i-(nums.length-k))];
+        	nums[nums.length-1-(i-(nums.length-k))] = val;
+        }
+        for(int i=0; i<(nums.length)/2; i++){
+        	val=nums[i];
+        	nums[i] = nums[nums.length-1-i];
+        	nums[nums.length-1-i] = val;
+//        	System.out.println(nums[i]);
+        }
+//        for(int i=0; i<nums.length; i++){
+//        	System.out.println(nums[i]);        	
+//        }
+        return;
+	}
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_242_050.java b/Week_01/id_50/LeetCode_242_050.java
new file mode 100644
index 00000000..3171b558
--- /dev/null
+++ b/Week_01/id_50/LeetCode_242_050.java
@@ -0,0 +1,54 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 有效的字母异位词
+ */
+public class LeetCode_242_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_242_050 solution = new LeetCode_242_050();
+		int[] nums = {1,2};
+		String[] strs = {"nozzle","punjabi","waterlogged","imprison","crux","numismatists"};
+		System.out.println(solution.isAnagram("dgqztusjuu", "dqugjzutss"));
+	}
+
+	public boolean isAnagram(String s, String t) {
+        if(s == null || t == null){
+			return false;
+		}
+		if(s.length() != t.length()){
+			return false;
+		}
+		Map<Object, Integer> map1 = new HashMap<>();
+		Map<Object, Integer> map2 = new HashMap<>();
+		for(int i=0; i<s.length(); i++){
+			if(map1.get(s.charAt(i)) != null){
+				map1.put(s.charAt(i), map1.get(s.charAt(i))+1);
+			}else{
+				map1.put(s.charAt(i), 1);				
+			}
+		}
+		for(int i=0; i<t.length(); i++){
+			if(map2.get(t.charAt(i)) != null){
+				map2.put(t.charAt(i), map2.get(t.charAt(i))+1);
+			}else{
+				map2.put(t.charAt(i), 1);				
+			}
+		}
+		
+		
+		return map1.equals(map2);
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_26_050.java b/Week_01/id_50/LeetCode_26_050.java
new file mode 100644
index 00000000..86281cdd
--- /dev/null
+++ b/Week_01/id_50/LeetCode_26_050.java
@@ -0,0 +1,48 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ *  删除排序数组中的重复项
+ */
+public class LeetCode_26_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_26_050 solution = new LeetCode_26_050();
+		int[] nums = {1,2};
+		System.out.println(solution.removeDuplicates(nums));
+	}
+
+	public int removeDuplicates(int[] nums) {
+		int n = 0;
+		for(int i=0; i<nums.length; i++){
+			for(int j=0; j<=n; j++){
+				if(i==0){
+//					System.out.println(nums[i]);
+					n++;
+					break;
+				}
+				if(nums[i]==nums[j]){
+					break;
+				}else{
+					if(j==(n-1)){
+						nums[n]=nums[i];
+//						System.out.println(nums[i]);
+						n++;
+					}
+				}
+			}
+		}
+        return n;
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_441_050.java b/Week_01/id_50/LeetCode_441_050.java
new file mode 100644
index 00000000..9e9b0e55
--- /dev/null
+++ b/Week_01/id_50/LeetCode_441_050.java
@@ -0,0 +1,41 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 排列硬币
+ */
+public class LeetCode_441_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_441_050 solution = new LeetCode_441_050();
+		System.out.println(solution.arrangeCoins(2147483647));
+	}
+
+	public int arrangeCoins(int n) {
+        if(n<=0){
+			return 0;
+		}
+		long i=1;
+		for (; i<=(n/2+1);i++){
+			long val = ((1+i)*i)/2;
+			if(val<=n){
+				continue;
+			}else{
+				break;
+			}
+		}
+		i--;
+		return Integer.valueOf(""+i);
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_49_050.java b/Week_01/id_50/LeetCode_49_050.java
new file mode 100644
index 00000000..cd0ca424
--- /dev/null
+++ b/Week_01/id_50/LeetCode_49_050.java
@@ -0,0 +1,47 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 字母异位词分组
+ */
+public class LeetCode_49_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_49_050 solution = new LeetCode_49_050();
+		String[] strs = {"nozzle","punjabi","waterlogged","imprison","crux","numismatists"};
+		solution.groupAnagrams(strs);
+	}
+
+	public List<List<String>> groupAnagrams(String[] strs) {
+        if( strs.length == 0 ){
+			return null;
+		}
+		Map<String, List> mapList = new HashMap<String, List>();
+		for(int i=0; i<strs.length; i++){
+			char[] charArr = strs[i].toCharArray();
+			Arrays.sort(charArr);
+			String sortStr = String.valueOf(charArr);
+			if(!mapList.containsKey(sortStr)){
+				List<String> listStr = new ArrayList<>();
+				listStr.add(strs[i]);
+				mapList.put(sortStr, listStr);
+			}else{
+				List<String> listStr = mapList.get(sortStr);
+				listStr.add(strs[i]);
+				mapList.put(sortStr, listStr);
+			}
+		}
+		return new ArrayList(mapList.values());
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_50/LeetCode_50_050.java b/Week_01/id_50/LeetCode_50_050.java
new file mode 100644
index 00000000..4f5b3381
--- /dev/null
+++ b/Week_01/id_50/LeetCode_50_050.java
@@ -0,0 +1,46 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+
+
+/**
+ * @author yu
+ * 实现 pow(x, n) ，即计算 x 的 n 次幂函数。
+ */
+public class LeetCode_50_050 {
+	/**
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		LeetCode_50_050 solution = new LeetCode_50_050();
+		System.out.println(solution.myPow(2, 10));
+	}
+
+	private double calPow(double x, int n) {
+		if(n==0){
+			return 1;
+		}
+		double half = calPow(x, n/2);
+		if(n%2 == 0){
+			return half*half;
+		}else{
+			return half*half*x;
+		}
+	}
+	public double myPow(double x, int n) {
+		if(n==0){
+			return 1;
+		}
+		if(n>0){
+			return calPow(x, n);
+		}else{
+			return 1/calPow(x, Math.abs(n));
+		}
+	}
+}
\ No newline at end of file