docs: 为 30 题添加说明

Signed-off-by: YdrMaster <[email protected]>

Author: YdrMaster

exercises/30_std_unique_ptr/main.cpp

@@ -1,4 +1,5 @@
 #include "../exercise.h"
+#include <cstring>
 #include <memory>
 #include <string>
 #include <vector>
@@ -22,21 +23,15 @@ class Resource {
 
 using Unique = std::unique_ptr<Resource>;
 Unique reset(Unique ptr) {
-    if (ptr) {
-        ptr->record('r');
-    }
+    if (ptr) ptr->record('r');
     return std::make_unique<Resource>();
 }
 Unique drop(Unique ptr) {
-    if (ptr) {
-        ptr->record('d');
-    }
+    if (ptr) ptr->record('d');
     return nullptr;
 }
 Unique forward(Unique ptr) {
-    if (ptr) {
-        ptr->record('f');
-    }
+    if (ptr) ptr->record('f');
     return ptr;
 }
 
@@ -57,6 +52,7 @@ int main(int argc, char **argv) {
     std::vector<const char *> answers[]{
         {"fd"},
         // TODO: 分析 problems[1] 中资源的生命周期，将记录填入 `std::vector`
+        // NOTICE: 此题结果依赖对象析构逻辑，平台相关，提交时以 CI 实际运行平台为准
         {"", "", "", "", "", "", "", ""},
         {"", "", "", "", "", "", "", ""},
     };