add solution of HW4

.vscode/settings.json

@@ -51,6 +51,26 @@
         "stdexcept": "cpp",
         "streambuf": "cpp",
         "typeinfo": "cpp",
-        "cassert": "cpp"
+        "cassert": "cpp",
+        "bitset": "cpp",
+        "charconv": "cpp",
+        "chrono": "cpp",
+        "codecvt": "cpp",
+        "condition_variable": "cpp",
+        "cstring": "cpp",
+        "ratio": "cpp",
+        "mutex": "cpp",
+        "semaphore": "cpp",
+        "span": "cpp",
+        "stop_token": "cpp",
+        "thread": "cpp",
+        "variant": "cpp",
+        "format": "cpp",
+        "__nullptr": "cpp",
+        "__bit_reference": "cpp",
+        "__hash_table": "cpp",
+        "__string": "cpp",
+        "queue": "cpp",
+        "stack": "cpp"
     }
 }