#811 Subdomain Visit Count

需要存重覆值，Map 真的好用

LeetCode

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.

input: 給一 count + domain 組成的陣列
output: 計算 subdomains 被拜訪了幾次，例如 "9001 discuss.leetcode.com" subdomain 也會被計算進去
"9001 discuss.leetcode.com"
"9001 leetcode.com"
"9001 com"

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.
*/

/**
 * @param {string[]} cpdomains
 * @return {string[]}
 */
var subdomainVisits = function(cpdomains) {

Edge Case

before 901 have space ?

如何解

本來想用 Regex 但是後來覺得直接遍歷一次效能更好。因為規則是

["9001 discuss.leetcode.com"]
================================
"9001 discuss.leetcode.com"
"9001 leetcode.com"
"9001 com"

所以我會先把 9001 抓出來。剩下 domain 會從後面開始存 count

var subdomainVisits = function(cpdomains) {
    let myMap = new Map();
    let final = []
    cpdomains.forEach( domain =>{
        // 先把 count 抓出來
        let result = domain.split(' ')
        let count = Number(result[0]);
        let len = result[1].length;
        // 開始抓 subdomain 然後把 count 存進 map
        for(let i = len; i > 0; i--){
            if(result[1][i] == '.'){
                myMap.set(result[1].substr(i + 1), !myMap.has(result[1].substr(i + 1)) ?  count : myMap.get(result[1].substr(i + 1)) + count)
            }
        }
        myMap.set(result[1], !myMap.has(result[1]) ?  count : myMap.get(result[1]) + count)
    })

    myMap.forEach( (item, index) =>{
        final.push(item + ' ' + index)
    })
    return final;
};

console.log(subdomainVisits(["900 google.mail.com", "50 yahoo.com", "1 intel.mail.com", "5 wiki.org"]));
//  faster than 80.99% of JavaScript online submissions