如何从多图获取密钥以获取价值

Question

I am having Mutimap which contains following data.

Reports = {UserName1=[report1,report2,report3], UserName2=[report4,report5],UserName3=[report6,report7,report8],UserName4=[report9]}

I want to getkey(report6) for specific value from Multimap, output UserName3

Answer 1

In guava , filterValues with your predicate , you can get the specified entries . Example:

    Multimaps.filterValues(testMultiMap, new Predicate<List<String>>() {
        @Override
        public boolean apply(List<String> strings) {
            return strings.contains("report6");
        }
    });

Answer 2

If you don't preprocess the data, a getkey() query need to scan all values in all keys to get the position. If you have n querys and the map has m values totally, the algorithm complexity will be O(n*m) .

If you preprocess the data, map the value and the key in a new map, such as newmap['report6'] = 'UserName3' , the algorithm complexity will be O(m+n) .

So, when you have many queries, you should choose the second approach.