feat: classroom problem

hw1/src/Classroom/Classroom.sol

@@ -4,9 +4,16 @@ pragma solidity ^0.8.0;
 /* Problem 1 Interface & Contract */
 contract StudentV1 {
     // Note: You can declare some state variable
+    bool reg = false;
 
     function register() external returns (uint256) {
         // TODO: please add your implementaiton here
+        if (reg) {
+            return 123;
+        } else {
+            reg = true;
+            return 1001;
+        }
     }
 }
 
@@ -18,6 +25,11 @@ interface IClassroomV2 {
 contract StudentV2 {
     function register() external view returns (uint256) {
         // TODO: please add your implementaiton here
+        if (IClassroomV2(msg.sender).isEnrolled()) {
+            return 123;
+        } else {
+            return 1001;
+        }
     }
 }
 
@@ -25,5 +37,11 @@ contract StudentV2 {
 contract StudentV3 {
     function register() external view returns (uint256) {
         // TODO: please add your implementaiton here
+        // return gasleft();
+        if (gasleft() > 7000) {
+            return 1001;
+        } else {
+            return 123;
+        }
     }
 }