LintCode: Unique Characters

C++,

time: O(n^2)

space: O(0)

class Solution {
public:
    /**
     * @param str: a string
     * @return: a boolean
     */
    bool isUnique(string &str) {
        // write your code here
        for (int i=0; i<str.size(); i++) {
            for (int j=i+1; j<str.size(); j++) {
                if (str[i] == str[j]) {
                    return false;
                }
            }
        }
        return true;
    }
};

C++,

time: O(n)

space: O(n)

class Solution {
public:
    /**
     * @param str: a string
     * @return: a boolean
     */
    bool isUnique(string &str) {
        // write your code here
        string tmp;
        for (int i=0; i<str.size(); i++) {
            if (-1 == tmp.find(str[i])) {
                tmp.push_back(str[i]);
            } else {
                return false;
            }
        }
        return true;
    }
};