811. Subdomain Visit Count (M)

Wayfair

A website domain "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.

A count-paired domain is a domain that has one of the two formats "rep d1.d2.d3" or "rep d1.d2" where rep is the number of visits to the domain and d1.d2.d3 is the domain itself.

• For example, "9001 discuss.leetcode.com" is a count-paired domain that indicates that discuss.leetcode.com was visited 9001 times.

Given an array of count-paired domains cpdomains, return an array of the count-paired domains of each subdomain in the input. You may return the answer in any order.

Example 1:

Input: cpdomains = ["9001 discuss.leetcode.com"]
Output: ["9001 leetcode.com","9001 discuss.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: cpdomains = ["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.

Constraints:

• 1 <= cpdomain.length <= 100

• 1 <= cpdomain[i].length <= 100

• cpdomain[i] follows either the "repi d1i.d2i.d3i" format or the "repi d1i.d2i" format.

• repi is an integer in the range [1, 104].

• d1i, d2i, and d3i consist of lowercase English letters.

Solution:

class Solution {
    private Map<String,Integer> map;
    public List<String> subdomainVisits(String[] cpdomains) {
        
        this.map = new HashMap<>();
        
        for(int i = 0; i< cpdomains.length; i++)
        {
            getSubDomainCount(cpdomains[i]);
        }
        return getOutput(map);
    }
    
    public void getSubDomainCount(String element)
    {
        //String[] array = element.split(" ");
        String[] array = element.split("\\s+");
        int count = Integer.valueOf(array[0]);
        String domain = array[1];
        //重点在这里，"." 要用 "\\." 表示。
        String[] domains = domain.split("\\.");
        
        String temp = "";
        for(int i = domains.length-1; i>=0; i--)
        {
            temp = domains[i] + (temp.equals("") ? temp : "." + temp);
            map.put(temp, map.getOrDefault(temp, 0) + count);    
        }
    }
                    
    
    public List<String> getOutput(Map<String, Integer> map)
    {
        List<String> res = new ArrayList<String>();
        for(Map.Entry<String, Integer> entry : map.entrySet())
        {
            StringBuilder sb = new StringBuilder();
            sb.append(entry.getValue())
                .append(" ")
                .append(entry.getKey());
            res.add(sb.toString());
        }
        return res;
    }
                    
}

简易版：

class Solution {
    public List<String> subdomainVisits(String[] cpdomains) {
        Map<String, Integer> counts = new HashMap();
        for (String domain: cpdomains) {
            String[] cpinfo = domain.split("\\s+");
            String[] frags = cpinfo[1].split("\\.");
            int count = Integer.valueOf(cpinfo[0]);
            String cur = "";
            for (int i = frags.length - 1; i >= 0; --i) {
                cur = frags[i] + (i < frags.length - 1 ? "." : "") + cur;
                counts.put(cur, counts.getOrDefault(cur, 0) + count);
            }
        }

        List<String> ans = new ArrayList();
        for (String dom: counts.keySet())
            ans.add("" + counts.get(dom) + " " + dom);
        return ans;
    }
}