diff --git a/Hash/3448.Count-Substrings-Divisible-By-Last-Digit/3448.Count-Substrings-Divisible-By-Last-Digit.cpp b/Hash/3448.Count-Substrings-Divisible-By-Last-Digit/3448.Count-Substrings-Divisible-By-Last-Digit.cpp
new file mode 100644
index 000000000..fd25aa2ae
--- /dev/null
+++ b/Hash/3448.Count-Substrings-Divisible-By-Last-Digit/3448.Count-Substrings-Divisible-By-Last-Digit.cpp
@@ -0,0 +1,43 @@
+using LL = long long;
+class Solution {    
+    int n;
+public:
+    long long countSubstrings(string s) 
+    {
+        n = s.size();
+        vector<int>nums;
+        for (auto ch: s)
+            nums.push_back(ch-'0');
+        nums.insert(nums.begin(), 0);
+        
+        LL ret = 0;
+        for (int k=1; k<=9; k++)
+            ret += helper(nums, k);        
+        return ret;
+    }
+    
+    LL helper(vector<int>&nums, int k)
+    {        
+        vector<LL>count(k, 0);
+        vector<LL>count2(k,0);
+        LL ret = 0;
+        
+        int r = 0;
+        count[0] = 1;
+        for (int i=1; i<=n; i++)
+        {                        
+            for (int d=0; d<k; d++)
+                count2[d] = 0;
+            for (int d=0; d<k; d++)
+                count2[(d*10)%k]+=count[d];
+            count = count2;
+            
+            r = (r*10+nums[i])%k;
+            if (nums[i]==k)            
+                ret += count[r];            
+            count[r]+=1;
+        }
+
+        return ret;
+    }
+};
diff --git a/Others/3447.Assign-Elements-to-Groups-with-Constraints/3447.Assign-Elements-to-Groups-with-Constraints.cpp b/Others/3447.Assign-Elements-to-Groups-with-Constraints/3447.Assign-Elements-to-Groups-with-Constraints.cpp
new file mode 100644
index 000000000..fb78c0a9f
--- /dev/null
+++ b/Others/3447.Assign-Elements-to-Groups-with-Constraints/3447.Assign-Elements-to-Groups-with-Constraints.cpp
@@ -0,0 +1,29 @@
+class Solution {    
+public:
+    vector<int> assignElements(vector<int>& groups, vector<int>& elements) 
+    {
+        int n = *max_element(groups.begin(), groups.end());
+        vector<int>arr(n+1, -1);
+        
+        for (int j=0; j<elements.size(); j++)
+        {            
+            int x0 = elements[j];
+            if (x0>n) continue;
+            
+            if (arr[x0]!=-1) continue;
+            
+            int x = x0;            
+            while (x<=n)
+            {
+                if (arr[x]==-1)
+                    arr[x] = j;
+                x+=x0;                    
+            }
+        }
+        
+        vector<int>rets;
+        for (int g: groups)
+            rets.push_back(arr[g]);
+        return rets;
+    }
+};
diff --git a/Others/3447.Assign-Elements-to-Groups-with-Constraints/Readme.md b/Others/3447.Assign-Elements-to-Groups-with-Constraints/Readme.md
new file mode 100644
index 000000000..3e6d9e611
--- /dev/null
+++ b/Others/3447.Assign-Elements-to-Groups-with-Constraints/Readme.md
@@ -0,0 +1,7 @@
+### 3447.Assign-Elements-to-Groups-with-Constraints
+
+突破点在于groups里的元素的数值不超过1e5.在这个范围是，如果枚举所有1的倍数，然后枚举所有2的倍数，然后枚举所有3的倍数，直至枚举n的倍数，那么总共的时间复杂度是`n+n/2+n/3+...n/n = n*(1+1/2+1/3+...1/n)`.这个级数虽然不收敛，但是它是趋近于nlog(n)的。所以本题可以用暴力枚举。
+
+所以本题的算法很简单。我们开一个长度为1e5的数组assign，来记录每个自然数最早能被哪个element所assign。我们依次考察element里的每个元素，比如说elements[j]=x，然后枚举x的所有倍数（直至1e5），比如说kx，那样就有`assign[kx] = j`，当然根据题意，我们对于每个assign我们只更新一次。
+
+最后根据groups的数值，从assgin里把答案拷贝过去即可。
diff --git a/Readme.md b/Readme.md
index 08acb0ac8..d99cd8366 100644
--- a/Readme.md
+++ b/Readme.md
@@ -211,6 +211,7 @@
 [2875.Minimum-Size-Subarray-in-Infinite-Array](https://github.com/wisdompeak/LeetCode/tree/master/Hash/2875.Minimum-Size-Subarray-in-Infinite-Array) (H-)      
 [2949.Count-Beautiful-Substrings-II](https://github.com/wisdompeak/LeetCode/tree/master/Hash/2949.Count-Beautiful-Substrings-II) (H-)      
 [2950.Number-of-Divisible-Substrings](https://github.com/wisdompeak/LeetCode/tree/master/Hash/2950.Number-of-Divisible-Substrings) (H-)      
+[3448.Count-Substrings-Divisible-By-Last-Digit](https://github.com/wisdompeak/LeetCode/tree/master/Hash/3448.Count-Substrings-Divisible-By-Last-Digit) (H-)      
 
 #### [Sorted Container](https://github.com/wisdompeak/LeetCode/tree/master/Sorted_Container)
 [220.Contains-Duplicate-III](https://github.com/wisdompeak/LeetCode/tree/master/Sorted_Container/220.Contains-Duplicate-III) (M)  
@@ -1631,6 +1632,7 @@
 [2768.Number-of-Black-Blocks](https://github.com/wisdompeak/LeetCode/tree/master/Others/2768.Number-of-Black-Blocks) (M+)      
 [2857.Count-Pairs-of-Points-With-Distance-k](https://github.com/wisdompeak/LeetCode/tree/master/Others/2857.Count-Pairs-of-Points-With-Distance-k) (M+)      
 [3404.Count-Special-Subsequences](https://github.com/wisdompeak/LeetCode/tree/master/Others/3404.Count-Special-Subsequences) (H)      
+[3447.Assign-Elements-to-Groups-with-Constraints](https://github.com/wisdompeak/LeetCode/tree/master/Others/3447.Assign-Elements-to-Groups-with-Constraints) (M+)      
 * ``Presum``   
 [1878.Get-Biggest-Three-Rhombus-Sums-in-a-Grid](https://github.com/wisdompeak/LeetCode/tree/master/Others/1878.Get-Biggest-Three-Rhombus-Sums-in-a-Grid) (M+)  
 [1906.Minimum-Absolute-Difference-Queries](https://github.com/wisdompeak/LeetCode/tree/master/Others/1906.Minimum-Absolute-Difference-Queries) (M+)