Longest Substring Without Repeating Characters

Author: applewjg

LongestSubstringWithoutRepeatingCharacters.java

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+/*
+ Author:     King, [email protected]
+ Date:       Dec 12, 2014
+ Problem:    Longest Substring Without Repeating Characters
+ Difficulty: Medium
+ Source:     https://oj.leetcode.com/problems/longest-substring-without-repeating-characters/
+ Notes:
+ Given a string, find the length of the longest substring without repeating characters. 
+ For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. 
+ For "bbbbb" the longest substring is "b", with the length of 1.
+
+ Solution: 1. Pay attention when moving the 'start' pointer forward.
+           2. More space, but maybe faster.
+ */
+public class Solution {
+    public int lengthOfLongestSubstring_1(String s) {
+        boolean[] hash = new boolean[256];
+        Arrays.fill(hash,false);
+        int n = s.length();
+        if (n <= 1) return n;
+        int start = 0, end = 0, res = 0;
+        while (end < n && start + res < n) {
+            if (hash[s.charAt(end)] == false) {
+                hash[s.charAt(end++)] = true;
+            } else {
+                hash[s.charAt(start++)] = false;
+            }
+            res = Math.max(res, end - start);
+        }
+        return res;
+    }
+    public int lengthOfLongestSubstring_2(String s) {
+        int[] hash = new int[256];
+        Arrays.fill(hash, -1);
+        int n = s.length();
+        if (n <= 1) return n;
+        hash[s.charAt(0)] = 0;
+        int start = 0, res = 1, cur = 0;
+        while (++cur < n) {
+            if (hash[s.charAt(cur)] >= start) {
+                start = hash[s.charAt(cur)] + 1;
+            }
+            res = Math.max(res, cur - start + 1);
+            hash[s.charAt(cur)] = cur;
+        }
+        return res;
+    }
+}