LintCode 判断字符串是否没有重复字符题目分析代码

public class Solution {
    /**
     * @param str: a string
     * @return: a boolean
     */
    public boolean isUnique(String str) {
        // write your code here
                Set set = new HashSet();
        for(int i=0;i<str.length();i++)
            if(set.add(str.charAt(i))==false)
                return false;
        return true;
    }
}

public class Solution {
    /**
     * @param str: a string
     * @return: a boolean
     */
    public boolean isUnique(String str) {
        // write your code here
        boolean[] char_set = new boolean[256];
        for (int i = 0; i < str.length(); i++) {
        int val = str.charAt(i);
        if (char_set[val]) return false;
            char_set[val] = true;
        }
        return true;
    }
}