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| /* | |
| * 1.1 Implement an algorithm to determine if a string has all unique characters | |
| * What if you cannot use additional data structures? | |
| * | |
| * 思路：假设输入是ascii字符，创建一个长度为256的array,遍历输入的字符串，若重复返回false，不重复返回true. | |
| * 特殊情况: null和空字符串都认为是unique的输入，即返回true.输入的字符串长度大于256，返回false. | |
| */ | |
| import java.io.*; | |
| class UniqueCharacters { | |
| public static boolean UniqueCharactersFinder(String s) { | |
| if (s == null || s.isEmpty()) { | |
| return true; | |
| } | |
| int len = s.length(); | |
| if (len > 256) { | |
| return false; | |
| } | |
| boolean[] ASCII_TABLE = new boolean[256]; //Default values are false | |
| for(int i = 0; i < len; i++) { | |
| char c = s.charAt(i); | |
| if (ASCII_TABLE[c]) { | |
| return false; | |
| } | |
| else { | |
| ASCII_TABLE[c] = true; | |
| } | |
| } | |
| return true; | |
| } | |
| public static void main(String[] args)throws Exception { | |
| System.out.println("Please type the string:"); | |
| BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); | |
| String s = reader.readLine(); | |
| if (UniqueCharactersFinder(s)) { | |
| System.out.println("String with unique characters!"); | |
| } | |
| else { | |
| System.out.println("String with repeat characters!"); | |
| } | |
| } | |
| } |
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