update 3._Longest_Substring_Without_Repeating_Characters.md

Author: Rishabh Jain

docs/Leetcode_Solutions/Java/3._Longest_Substring_Without_Repeating_Characters.md

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+
+### 3. Longest Substring Without Repeating Characters
+
+题目:
+https://leetcode.com/problems/longest-substring-without-repeating-characters/
+
+难度:
+Medium
+
+```java
+class Solution {
+    public int lengthOfLongestSubstring(String s) {
+        int stIdx = 0, maxLen = 0;
+        int arr[] = new int[128];
+        for(int i=0;i<s.length();i++){
+            stIdx = Math.max(arr[s.charAt(i)],stIdx);
+            maxLen = Math.max(maxLen, i-stIdx+1);
+            arr[s.charAt(i)] = i+1;
+        }
+        return maxLen;
+    }
+}
+```java