diff --git a/cpp/LFU-LRU.cpp b/cpp/LFU-LRU.cpp
index c58cf21..70d45ad 100644
--- a/cpp/LFU-LRU.cpp
+++ b/cpp/LFU-LRU.cpp
@@ -1,4 +1,5 @@
-#include <bits/stdc++.h>
+#include <unordered_map>
+#include <vector>
 using namespace std;
 
 /**
@@ -90,7 +91,11 @@ class LFUCache {
   void put(int key, int value) {
     if (size == 0) return;
     if (get(key) != -1) {
-      cache[key]->val = value;
+      Node* node = cache[key];
+      node->val = value;
+      node->freq++;
+      deleteNode(node);
+      addHead(node);
     } else {
       if (cache.size() == size) {
         popTail();
@@ -160,7 +165,7 @@ class LRUCache {
     node->prev->next = node->next;
   }
 
-  Node* popTail() {
+  void popTail() {
     Node* node = tail->prev;
     deleteNode(node);
     cache.erase(node->key);
diff --git a/daily/Aug30.cc b/daily/Aug30.cc
new file mode 100644
index 0000000..719c054
--- /dev/null
+++ b/daily/Aug30.cc
@@ -0,0 +1,26 @@
+#include <vector>
+using namespace std;
+
+class Solution {
+ public:
+ /**
+  * @brief LC3153: Sum of digit diffs of all pairs
+  * Time: O(NlogU), Space: O(DlogU), D = 10
+  *
+  * @param nums
+  * @return long long
+  */
+  long long sumDigitDifferences(vector<int>& nums) {
+    long long len = nums.size(), m = to_string(nums[0]).length();
+    long long ans = m * len * (len - 1) / 2;
+    vector<array<int, 10>> cnt(m);
+    for (int x : nums) {
+      for (int i = 0; x; x /= 10) {
+        ans -= cnt[i++][x %= 10]++;
+      }
+    }
+
+    return ans;
+  }
+
+};