diff --git a/Strings/slides/hashes/codes/double_hash.cpp b/Strings/slides/hashes/codes/double_hash.cpp
index 676d4ee8..e7d890c0 100644
--- a/Strings/slides/hashes/codes/double_hash.cpp
+++ b/Strings/slides/hashes/codes/double_hash.cpp
@@ -6,12 +6,13 @@ int f(char c) { return c - 'a' + 1; }
 
 int hi(long long pi, long long qi, const string& s)
 {
+    int N = s.size();
     long long ans = 0;
 
-    for (auto c : s)
+    for (int i = N - 1; i >= 0; --i)
     {
         ans = (ans * pi) % qi;
-        ans = (ans + f(c)) % qi;
+        ans = (ans + f(s[i])) % qi;
     }
 
     return ans;
diff --git a/Strings/slides/hashes/codes/h.cpp b/Strings/slides/hashes/codes/h.cpp
index 7f3b1e5c..04f25e11 100644
--- a/Strings/slides/hashes/codes/h.cpp
+++ b/Strings/slides/hashes/codes/h.cpp
@@ -5,12 +5,13 @@ int f(char c)
 
 int h(const string& s)
 {
+    int N = s.size();
     long long ans = 0, p = 31, q = 1'000'000'007;
 
-    for (auto c : s)
+    for (int i = N - 1; i >= 0; --i)
     {
         ans = (ans * p) % q;
-        ans = (ans + f(c)) % q;
+        ans = (ans + f(s[i])) % q;
     }
 
     return ans;
diff --git a/Strings/slides/hashes/codes/subs.cpp b/Strings/slides/hashes/codes/subs.cpp
index 0f5fed87..f97f70a7 100644
--- a/Strings/slides/hashes/codes/subs.cpp
+++ b/Strings/slides/hashes/codes/subs.cpp
@@ -11,12 +11,13 @@ int f(char c)
 
 int h(const string& s)
 {
+    int N = s.size();
     ll ans = 0;
 
-    for (auto c : s)
+    for (int i = N - 1; i >= 0; --i)
     {
         ans = (ans * p) % q;
-        ans = (ans + f(c)) % q;
+        ans = (ans + f(s[i])) % q;
     }
 
     return ans;
@@ -72,8 +73,8 @@ int h(int i, int j, const vector<ll>& ps, const vector<ll>& is)
 
 int unique_substrings(const string& s)
 {
-    set<ll> hs;
     int N = s.size();
+    set<ll> hs;
 
     auto ps = prefixes(s);
     auto is = inverses(s.size());