diff --git a/C++/chapLinearList.tex b/C++/chapLinearList.tex
index 6068e18b..c8da67f9 100644
--- a/C++/chapLinearList.tex
+++ b/C++/chapLinearList.tex
@@ -455,7 +455,7 @@ \subsubsection{代码}
         }
         for (int i = 0; i < num.size(); i++) {
             const int gap = target - num[i];
-            if (mapping.find(gap) != mapping.end()) {
+            if (mapping.find(gap) != mapping.end() && mapping[gap] > i) {
                 result.push_back(i + 1);
                 result.push_back(mapping[gap] + 1);
                 break;