diff --git a/src/test.cpp b/src/test.cpp
index 7af0f17..e1ca8b6 100644
--- a/src/test.cpp
+++ b/src/test.cpp
@@ -3,7 +3,7 @@ using namespace std;
 
 class Solution {
 public:
-    vector<int> findDiagonalOrder(vector<vector<int>>& m) {
+    vector<int> findDiagonalOrder(const vector<vector<int>>& m) {
         int x=0,y=0;
         bool isup=true;
         vector<int> res;