feat: enhance Codeforces URL handling with contest and problem set ex…

src/platform/codeforces/codeforces.go

@@ -10,6 +10,13 @@ import (
 const urlFormat string = "https://codeforces.com/problemset/problem/%s/%s"
 const codeNameDelimiter string = "-"
 
+const (
+	ProblemSet = "problemset"
+	Contest    = "contest"
+)
+
+var ErrInvaliidCodeforcesUrl = errors.New("invalid url")
+
 type CodeforcesInstance struct {
 	name     types.PlatformName
 	codeName string
@@ -25,12 +32,27 @@ func (cf CodeforcesInstance) GetCodeName() string {
 
 // This is the main method
 func GetInstance(url string) (types.Instance, error) {
+	// For codeforces either the problem could be from
+	// problem set or contest like below
+
+	url = strings.ToLower(url)
+
 	// extract code name from url
-	// example: https://codeforces.com/problemset/problem/1234/A
+	// example1 [problemset]: https://codeforces.com/problemset/problem/1234/A
+	// example2 [contest]: https://codeforces.com/contest/2236/problem/D
 
 	// if delimiter is "-"
-	// code name is 1234-A
-	extractedCodeName, err := extractCodeName(url)
+	// code name is 1234-A [example1]
+	// or name is 2236-D [example2]
+
+	var extractedCodeName string = ""
+	var err error
+	if strings.Contains(url, ProblemSet) {
+		extractedCodeName, err = extractCodeNameProblemSet(url)
+	} else {
+		extractedCodeName, err = extractCodeNameContest(url)
+	}
+
 	if err != nil {
 		return nil, err
 	}
@@ -41,10 +63,35 @@ func GetInstance(url string) (types.Instance, error) {
 	}, nil
 }
 
-func extractCodeName(url string) (string, error) {
+func extractCodeNameContest(url string) (string, error) {
+	// https://codeforces.com/contest/2236/problem/D
+	// first %s comes at index 42
+	if len("codeforces.com/contest/?/problem/?") > len(url) {
+		return "", ErrInvaliidCodeforcesUrl
+	}
+
+	index := strings.Index(url, Contest)
+	if index < 0 {
+		return "", ErrInvaliidCodeforcesUrl
+	}
+
+	index += len(Contest) + len("/")
+
+	// now the index is at contest Id
+	substring := url[index:]
+
+	split := strings.Split(substring, "/")
+
+	contestCode := string(split[0])
+	problem := strings.ToUpper(string(split[2]))
+
+	return contestCode + codeNameDelimiter + problem, nil
+}
+
+func extractCodeNameProblemSet(url string) (string, error) {
 	// first %s comes at index 42
 	if len(url) < 43 {
-		return "", errors.New("invalid url")
+		return "", ErrInvaliidCodeforcesUrl
 	}
 
 	prefixRemovedString := url[42:]