diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC12.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC12.java
new file mode 100644
index 00000000..38f42305
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC12.java	
@@ -0,0 +1,17 @@
+class Solution {
+    private static final int[] values = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
+    private static final String[] symbols = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
+
+    public String intToRoman(int num) {
+        StringBuilder sb = new StringBuilder();
+        // Loop through each symbol, stopping if num becomes 0.
+        for (int i = 0; i < values.length && num > 0; i++) {
+            // Repeat while the current symbol still fits into num.
+            while (values[i] <= num) {
+                num -= values[i];
+                sb.append(symbols[i]);
+            }
+        }
+        return sb.toString();
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC13.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC13.java
new file mode 100644
index 00000000..45e4c11c
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC13.java	
@@ -0,0 +1,40 @@
+class Solution {
+
+    static Map<String, Integer> values = new HashMap<>();
+
+    static {
+        values.put("M", 1000);
+        values.put("D", 500);
+        values.put("C", 100);
+        values.put("L", 50);
+        values.put("X", 10);
+        values.put("V", 5);
+        values.put("I", 1);
+    }
+
+    public int romanToInt(String s) {
+
+        int sum = 0;
+        int i = 0;
+        while (i < s.length()) {
+            String currentSymbol = s.substring(i, i + 1);
+            int currentValue = values.get(currentSymbol);
+            int nextValue = 0;
+            if (i + 1 < s.length()) {
+                String nextSymbol = s.substring(i + 1, i + 2);
+                nextValue = values.get(nextSymbol);
+            }
+
+            if (currentValue < nextValue) {
+                sum += (nextValue - currentValue);
+                i += 2;
+            }
+            else {
+                sum += currentValue;
+                i += 1;
+            }
+
+        }
+        return sum;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC136.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC136.java
new file mode 100644
index 00000000..1d76f476
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC136.java	
@@ -0,0 +1,14 @@
+class Solution {
+    public int singleNumber(int[] nums) {
+        HashMap<Integer, Integer> hash_table = new HashMap<>();
+        for (int i : nums) {
+            hash_table.put(i, hash_table.getOrDefault(i, 0) + 1);
+        }
+        for (int i : nums) {
+            if (hash_table.get(i) == 1) {
+                return i;
+            }
+        }
+        return 0;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC166.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC166.java
new file mode 100644
index 00000000..d42cddb1
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC166.java	
@@ -0,0 +1,12 @@
+//You must implement a solution with a/linear runtime/complexity and use only
+//constant extra space.
+//a⊕0=a  ;  a⊕a=0  ; a⊕b⊕a=(a⊕a)⊕b=0⊕b=b
+class Solution {
+    public int singleNumber(int[] nums) {
+        int a = 0;
+        for (int i : nums) {
+            a ^= i;
+        }
+        return a;
+    }
+}
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC172.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC172.java
new file mode 100644
index 00000000..328c81b1
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC172.java	
@@ -0,0 +1,17 @@
+//option 1 time limit exceeded
+import java.math.BigInteger;
+class Solution {
+    public int trailingZeroes(int n) {
+        int res = 0;
+        BigInteger Fac = BigInteger.ONE;
+        for(int i = 2; i <= n; i++){
+            Fac = Fac.multiply(BigInteger.valueOf(i));
+        }
+        while(Fac.mod(BigInteger.TEN).equals(BigInteger.ZERO)){
+            Fac = Fac.divide(BigInteger.TEN);
+            res += 1;
+        }
+        return res;
+    }
+}
+//option 2
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC190.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC190.java
new file mode 100644
index 00000000..ff2838ef
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC190.java	
@@ -0,0 +1,11 @@
+public class Solution {
+    public int reverseBits(int n) {
+        int ans = 0;
+        for (int i = 0; i < 32; i++) {
+            ans <<= 1;
+            ans = ans | (n & 1);
+            n >>= 1;
+        }
+        return ans;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC191.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC191.java
new file mode 100644
index 00000000..860c22f4
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC191.java	
@@ -0,0 +1,11 @@
+public int hammingWeight(int n) {
+        int bits = 0;
+        int mask = 1;
+        for (int i = 0; i < 32; i++) {
+        if ((n & mask) != 0) {
+        bits++;
+        }
+        mask <<= 1;
+        }
+        return bits;
+        }
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC217.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC217.java
new file mode 100644
index 00000000..9a48775a
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC217.java	
@@ -0,0 +1,12 @@
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> hashset = new HashSet<>(nums.length);
+        for (int x : nums){
+            if(hashset.contains(x)){
+                return true;
+            }
+            hashset.add(x);
+        }
+        return false;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC219.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC219.java
new file mode 100644
index 00000000..b8576445
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC219.java	
@@ -0,0 +1,13 @@
+class Solution {
+    public boolean containsNearbyDuplicate(int[] nums, int k) {
+        Set<Integer> set = new HashSet<>();
+        for (int i = 0; i < nums.length; ++i) {
+            if (set.contains(nums[i])) return true;
+            set.add(nums[i]);
+            if (set.size() > k) {
+                set.remove(nums[i - k]);
+            }
+        }
+        return false;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC220.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC220.java
new file mode 100644
index 00000000..7a6792f3
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC220.java	
@@ -0,0 +1,20 @@
+class Solution {
+    public boolean containsNearbyAlmostDuplicate(int[] nums, int k, int t) {
+        TreeSet<Integer> set = new TreeSet<>();
+        for (int i = 0; i < nums.length; ++i) {
+            // Find the successor of current element
+            Integer s = set.ceiling(nums[i]);
+            if (s != null && (long) s <= nums[i] + t) return true;
+
+            // Find the predecessor of current element
+            Integer g = set.floor(nums[i]);
+            if (g != null && nums[i] <= (long) g + t) return true;
+
+            set.add(nums[i]);
+            if (set.size() > k) {
+                set.remove(nums[i - k]);
+            }
+        }
+        return false;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC231.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC231.java
new file mode 100644
index 00000000..2bb52194
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC231.java	
@@ -0,0 +1,17 @@
+class Solution {
+    public boolean isPowerOfTwo(int n) {
+        if(n == 0){
+            return false;
+        }
+        if(n == 1){
+            return true;
+        }
+        if(n%2 != 0){
+            return false;
+        }
+        while(n%2 == 0){
+            n /= 2;
+        }
+        return n == 1;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC69.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC69.java
new file mode 100644
index 00000000..08a7b671
--- /dev/null
+++ b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Bit & Number & Math/LC69.java	
@@ -0,0 +1,9 @@
+class Solution {
+    public int mySqrt(int x) {
+        if (x < 2) return x;
+
+        int left = mySqrt(x >> 2) << 1;
+        int right = left + 1;
+        return (long)right * right > x ? left : right;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Java Basic& Design/test.java b/src/main/java/com/techbow/homework/y2021/m10/LianjiangHe/Java Basic& Design/test.java
new file mode 100644
index 00000000..e69de29b