387. First Unique Character in a String

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.

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2 passes

class Solution {
    public int firstUniqChar(String s) {
        Map<Character, Integer> map = new HashMap<>();
        
        for (int i = 0; i < s.length(); i++) {
            map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0) + 1);
        }
        
        for (int i = 0; i < s.length(); i++) {
            if (map.get(s.charAt(i)) == 1) return i;
        }
        
        return -1;
    }
}

Just for grins, 1 pass的方法可以考虑用set ＋LinkedHashMap, LinkedHashMap default的特性是保证key insertion order, Java doc