diff --git a/src/P2822/P2822_prefix.cpp b/src/P2822/P2822_prefix.cpp
index fee7f56..0d791d5 100644
--- a/src/P2822/P2822_prefix.cpp
+++ b/src/P2822/P2822_prefix.cpp
@@ -1,11 +1,19 @@
+#define NDEBUG
 #include <cctype>
 #include <iostream>
 #include <algorithm>
 #include <type_traits>
 
+#define NV(v)#v<<" : "<<(v)
+#ifdef NDEBUG
+    #define DEBUG(code)
+#else
+    #define DEBUG(code){code}
+#endif
 using ull = unsigned long long;
 
 static const size_t max_n {(size_t)2e3+5}; 
+// static const size_t max_n {(size_t)10}; 
 static ull k, c[max_n][max_n], prefix[max_n][max_n], t, n, m;
 
 static void init(){
@@ -16,16 +24,32 @@ static void init(){
             c[i][j] = (c[i-1][j-1] + c[i-1][j])%k;
         }
     }
+    DEBUG(
+        for(ull i{0};i<max_n;i++){
+            for(ull j{0};j<=i;j++){
+                std::cout<<c[i][j]<<' ';
+            }
+            std::cout<<'\n';
+        }
+        std::cout<<"===========\n";
+    )
+    
     for(ull i = 2;i<max_n-1;i++){ //注意这里是max_n-1
         for(ull j{1};j<=i;j++){
             prefix[i][j] = prefix[i-1][j]+prefix[i][j-1]-prefix[i-1][j-1] + (c[i][j]==0?1:0);
-        }
+        } 
         prefix[i][i+1] = prefix[i][i];
     }
+    DEBUG(
+        for(ull i{0};i<max_n;i++){
+            for(ull j{0};j<=i;j++){
+                std::cout<<prefix[i][j]<<' ';
+            }
+            std::cout<<'\n';
+        }
+    )
 }
 
-#define NV(v)#v<<" : "<<(v)
-
 template<class T>
 struct ReadNumber{
     ReadNumber& operator>>(T &num){