811. Subdomain Visit Count

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.

题目大意:统计访问子域名的次数

思路:遍历每个域名及其子域名,将其访问次数保存到map里

Java实现:

public List<String> subdomainVisits(String[] cpdomains) {
    Map<String, Integer> map = new HashMap<>();
    for (String str : cpdomains) {
        String[] arr = str.split(" ");
        int baseCount = Integer.parseInt(arr[0]);
        String tmpSub = arr[1];
        int fromIndex = 0;
        while (fromIndex != -1) {
            // System.out.println(fromIndex);
            String subDomain = tmpSub.substring(fromIndex + (fromIndex != 0 ? 1 : 0));
            Integer oldCount = map.get(subDomain) == null ? 0 : map.get(subDomain);
            map.put(subDomain, oldCount + baseCount);
            fromIndex = tmpSub.indexOf(".", fromIndex + 1);
        }
    }

    List<String> retList = new ArrayList<>();
    for (Map.Entry<String, Integer> entry : map.entrySet()) {
        retList.add(entry.getValue() + " " + entry.getKey());
    }
    return retList;
}