leetcode 387. First Unique Character in a String

Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.

---

 

class Solution(object):
    def firstUniqChar(self, s):
        """
        :type s: str
        :rtype: int
        """
        cnt = collections.Counter(s)
        for i,c in enumerate(s):
            if cnt[c] == 1:
                return i
        return -1

java 里还可以，直接一次扫描s搞定：

class Solution {
    public int firstUniqChar(String s) {
        Map<Character, Integer> map = new LinkedHashMap<>();
        Set<Character> set = new HashSet<>();
        for (int i = 0; i < s.length(); i++) {
            if (set.contains(s.charAt(i))) {
                if (map.get(s.charAt(i)) != null) {
                    map.remove(s.charAt(i));
                }
            } else {
                map.put(s.charAt(i), i);
                set.add(s.charAt(i));
            }
        }
        return map.size() == 0 ? -1 : map.entrySet().iterator().next().getValue();
    }
}

因为map里entryset保存了add顺序？？？