【leetcode】929. Unique Email Addresses

class Solution {
    public int numUniqueEmails(String[] emails) {
        List finalEmails = new ArrayList();
        
        for(String email : emails) {
            char[] chs = email.toCharArray();
            boolean afterPlussignAndBeforeAt = false;
            boolean beforeAt = true;
            StringBuffer sb = new StringBuffer();
            for(char ch : chs) {
                if(afterPlussignAndBeforeAt && ch != '@')
                    continue;
            
                if(ch == '@') {
                    afterPlussignAndBeforeAt = false;
                    beforeAt = false;
                }
                    
                if(ch == '+')
                    afterPlussignAndBeforeAt = true;
                if(!afterPlussignAndBeforeAt) {
                    if(ch == '.' && beforeAt)
                        continue;
                    sb.append(ch);
                }
            }
            if(!finalEmails.contains(sb.toString())) {
                finalEmails.add(sb.toString());
            }
        }
        return finalEmails.size();
    }
}

注：也可以使用split方法，将@前后两部分分解，分别处理。

    public int numUniqueEmails(String[] emails) {
        Set<String> normalized = new HashSet<>(); // used to save simplified email address, cost O(n) sapce.
        for (String email : emails) {
            String[] parts = email.split("@"); // split into local and domain parts.
            String[] local = parts[0].split("\\+"); // split local by '+'.
            normalized.add(local[0].replace(".", "") + "@" + parts[1]); // remove all '.', and concatenate '@' and domain.        
        }
        return normalized.size();
    }