Update LongestSubstring.java

Author: carpeventus

code/offer/src/Chap5/LongestSubstring.java

@@ -5,50 +5,34 @@
  * 假设字符串中只包含'a'~'z'之间的字符，例如在字符串"arabcacfr"中，最长的不含重复字符的子字符串是"acfr"，长度为4
  */
 public class LongestSubstring {
-    public int findLongestSubstring(String str) {
+      public  int lengthOfLongestSubstring(String str) {
+        if (str == null || str.length() == 0) return 0;
         int curLen = 0;
         int maxLen = 0;
         // 0~25表示a~z，position[0] = index,表明a上次出现在index处
-        int[] position = new int[26];
-        for (int i = 0; i < 26; i++) {
+        int[] position = new int[256];
+        for (int i = 0; i < 256; i++) {
             position[i] = -1;
         }
 
         for (int i = 0; i < str.length(); i++) {
-            int preIndex = position[str.charAt(i) - 'a'];
+            int preIndex = position[str.charAt(i)];
             // 字符第一次出现，或者d > f(i -1)
             if (preIndex == -1 || i - preIndex > curLen) curLen++;
             // d <= f(i -1) 
-            else curLen = i - preIndex;
+            else {
+                curLen = i - preIndex;
+            }
             // 记录当前字符出现的位置
-            position[str.charAt(i) - 'a'] = i;
+            position[str.charAt(i)] = i;
             if (curLen > maxLen) maxLen = curLen;
         }
         return maxLen;
-    }
 
-    public int findLongestSubstring2(String str) {
-        int curLen = 0;
-        int maxLen = 0;
-        int preIndex = -1;
-        // 0~25表示a~z，position[0] = index,表明a上次出现在index处
-        int[] position = new int[26];
-        for (int i = 0; i < 26; i++) {
-            position[i] = -1;
-        }
-
-        for (int i = 0; i < str.length(); i++) {
-            preIndex = Math.max(preIndex, position[str.charAt(i) - 'a']);
-			curLen = i - preIndex;
-            // 记录当前字符出现的位置
-            position[str.charAt(i) - 'a'] = i;
-            maxLen = Math.max(curLen, maxLen);
-        }
-        return maxLen;
     }
 
     public static void main(String[] args) {
         LongestSubstring l = new LongestSubstring();
-        System.out.println(l.findLongestSubstring("abcdefaz"));
+        System.out.println(l.lengthOfLongestSubstring("abcdefaz"));
     }
 }