LeetCode-Subdomain Visit Count

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Description：
A website domain like “discuss.leetcode.com” consists of various subdomains. At the top level, we have “com”, at the next level, we have “leetcode.com”, and at the lowest level, “discuss.leetcode.com”. When we visit a domain like “discuss.leetcode.com”, we will also visit the parent domains “leetcode.com” and “com” implicitly.

Now, call a “count-paired domain” to be a count (representing the number of visits this domain received), followed by a space, followed by the address. An example of a count-paired domain might be “9001 discuss.leetcode.com”.

We are given a list cpdomains of count-paired domains. We would like a list of count-paired domains, (in the same format as the input, and in any order), that explicitly counts the number of visits to each subdomain.

Example 1:

Input: 
["9001 discuss.leetcode.com"]
Output: 
["9001 discuss.leetcode.com", "9001 leetcode.com", "9001 com"]
Explanation: 
We only have one website domain: "discuss.leetcode.com". As discussed above, the subdomain "leetcode.com" and "com" will also be visited. So they will all be visited 9001 times.

Example 2:

Input: 
["900 google.mail.com", "50 yahoo.com", "1 intel.mail.com", "5 wiki.org"]
Output: 
["901 mail.com","50 yahoo.com","900 google.mail.com","5 wiki.org","5 org","1 intel.mail.com","951 com"]
Explanation: 
We will visit "google.mail.com" 900 times, "yahoo.com" 50 times, "intel.mail.com" once and "wiki.org" 5 times. For the subdomains, we will visit "mail.com" 900 + 1 = 901 times, "com" 900 + 50 + 1 = 951 times, and "org" 5 times.

Notes:

• The length of cpdomains will not exceed 100.
• The length of each domain name will not exceed 100.
• Each address will have either 1 or 2 “.” characters.
• The input count in any count-paired domain will not exceed 10000.
• The answer output can be returned in any order.

题意：给定一个字符串数组，数组中得每个字符串表示一个网站得域名及访问的次数，现要求计算所有的网站及子网总的访问次数；

解法：我们可以利用哈希表来存储每个网址的访问次数，按要求遍历字符串数组，对每个字符串利用空格划分访问次数及网址；每个网址中包含一个或者两个‘.’，我们可以利用’.'来找出所有的子域名；

Java

class Solution {
    public List<String> subdomainVisits(String[] cpdomains) {
        Map<String, Integer> table = new HashMap<>();
        List<String> result = new ArrayList<>();
        
        for (String cpdomain : cpdomains) {
            int times = Integer.valueOf(cpdomain.substring(0, cpdomain.indexOf('\u0020')));
            String domains = cpdomain.substring(cpdomain.indexOf('\u0020') + 1);
            int dotIndex = 0;
            while (dotIndex != -1) {
                String domain = dotIndex == 0 ? domains.substring(dotIndex) : domains.substring(++dotIndex);
                table.put(domain, table.getOrDefault(domain, 0) + times);
                dotIndex = domains.indexOf('.', dotIndex);
            }
        }
        for (String domain : table.keySet()) {
            result.add(table.get(domain) + " " + domain);
        }
        
        return result;
    }
}