[LintCode] Unique Characters

DevWiki 發(fā)布于2019-08-14 15:22 / 2697人閱讀

摘要：用做，十分簡單。如果不使用之外的數(shù)據(jù)結(jié)構(gòu)的話，可以用來做。不過只能過純字母字符的。

Problem

Implement an algorithm to determine if a string has all unique characters.

Example

Given "abc", return true.

Given "aab", return false.

Challenge

What if you can not use additional data structures?

Note

用HashSet做，十分簡單。
如果不使用String之外的數(shù)據(jù)結(jié)構(gòu)的話，可以用bit manipulation來做。不過只能過純字母字符的testcase。

Solution

public class Solution {
    public boolean isUnique(String str) {
        HashSet set = new HashSet();
        for (int i = 0; i < str.length(); i++) {
            if (!set.contains(str.charAt(i))) {
                set.add(str.charAt(i));
            }
            else return false;
        }
        return true;
    }
}

public class Solution {
    public boolean isUnique(String s) {
        int checker = 0;
        for (int i = 0; i < s.length(); i++) {
            int cur = s.charAt(i) - "a";
            if ((checker & (1 << cur)) > 0) {
                return false;
            }
            checker |= 1 << cur;
        }
        return true;
    }
}

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