"Longest Duplicate Substring" accepted solution, involving binary search and a map

1044-longest-duplicate-substring.go

@@ -290,6 +290,51 @@ func LongestDupSubstringGoroutines(s string) string {
 	return res
 }
 
-func LongestDupSubstring(s string) string {
-	return LongestDupSubstringGoroutines(s)
+func DupSubstringLengthN(s string, n int) string {
+	StringMap := map[string]interface{}{}
+
+	for begin := 0; begin <= len(s)-n; begin++ {
+		end := begin + n
+		str := s[begin:end]
+
+		_, ok := StringMap[str]
+		if ok {
+			return str
+		}
+
+		StringMap[str] = nil
+	}
+
+	return ""
+}
+
+func LongestDupSubstringBinarySearchAndMap(s string) string {
+	maxLen := 0
+	dups := map[int]string{}
+	dups[0] = ""
+
+	left := 0
+	right := len(s)
+	mid := 0
+
+	for left < right {
+		mid = (left + right) / 2
+		res := DupSubstringLengthN(s, mid)
+
+		if len(res) > 0 {
+			dups[mid] = res
+			left = mid + 1
+			if mid > maxLen {
+				maxLen = mid
+			}
+		} else {
+			right = mid
+		}
+	}
+
+	return dups[maxLen]
+}
+
+func LongestDupSubstring(s string) string {
+	return LongestDupSubstringBinarySearchAndMap(s)
 }