diff --git a/Arrays/largest_substr_wo_repetition.cpp b/Arrays/largest_substr_wo_repetition.cpp
new file mode 100644
index 0000000..23d6047
--- /dev/null
+++ b/Arrays/largest_substr_wo_repetition.cpp
@@ -0,0 +1,34 @@
+#include <iostream>
+
+int count [257];
+
+std::string findLargestSubstr(const std::string &str){
+	// start of current substr, and end of current substr
+	int s = 0, e = 0;
+	int maxs=0, maxe=0;
+
+	while (s < str.size()){
+		while (count[str[e]] == 0 && e < str.size()){
+			count[str[e]] ++;
+			e++;
+		}
+		if (e-s > maxe - maxs){
+			maxs = s;
+			maxe = e;
+		}
+		count[str[s]] --;
+		s++;
+	}
+
+	return str.substr(maxs, maxe - maxs);
+}
+
+int main(){
+	std::cout << "Input string: \n";
+	std::string str;
+	std::cin >> str;
+
+	std::cout << findLargestSubstr(str) << "\n";
+
+	return 0;
+}