solve 3: longest substring without repeating characters

Author: andavid

vscode/3.longest-substring-without-repeating-characters.java

@@ -0,0 +1,74 @@
+import java.util.HashSet;
+import java.util.Set;
+
+/*
+ * @lc app=leetcode id=3 lang=java
+ *
+ * [3] Longest Substring Without Repeating Characters
+ *
+ * https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
+ *
+ * algorithms
+ * Medium (27.96%)
+ * Total Accepted:    849.6K
+ * Total Submissions: 3M
+ * Testcase Example:  '"abcabcbb"'
+ *
+ * Given a string, find the length of the longest substring without repeating
+ * characters.
+ * 
+ * 
+ * Example 1:
+ * 
+ * 
+ * Input: "abcabcbb"
+ * Output: 3 
+ * Explanation: The answer is "abc", with the length of 3. 
+ * 
+ * 
+ * 
+ * Example 2:
+ * 
+ * 
+ * Input: "bbbbb"
+ * Output: 1
+ * Explanation: The answer is "b", with the length of 1.
+ * 
+ * 
+ * 
+ * Example 3:
+ * 
+ * 
+ * Input: "pwwkew"
+ * Output: 3
+ * Explanation: The answer is "wke", with the length of 3. 
+ * ⁠            Note that the answer must be a substring, "pwke" is a
+ * subsequence and not a substring.
+ * 
+ * 
+ * 
+ * 
+ */
+class Solution {
+  public int lengthOfLongestSubstring(String s) {
+    int len = s.length();
+    if (len < 2) {
+      return len;
+    }
+
+    int max = 0;
+    Set<Character> set = new HashSet<>();
+    
+    for (int fast = 0, slow = 0; fast < len; fast++) {
+      while (set.contains(s.charAt(fast))) {
+        set.remove(s.charAt(slow));
+        slow++;
+      }
+      set.add(s.charAt(fast));
+      max = Math.max(max, fast - slow + 1);
+    }
+
+    return max;
+  }
+}
+