Add Solution2.java to problems 0003

Author: huaxu1024

Diff for: solution/0003.Longest Substring Without Repeating Characters/Solution2.java

@@ -0,0 +1,13 @@
+class Solution {
+    public int lengthOfLongestSubstring(String s) {
+        int i = 0, j = 0, length = s.length(), max = 0;
+        Set<Character> set = new HashSet<>();
+        while (i < length && j < length) {
+            if (!set.contains(s.charAt(i))) {
+                set.add(s.charAt(i++));
+                max = Math.max(max, i - j);
+            } else set.remove(s.charAt(j++));
+        }
+        return max;
+    }
+}