亚麻卖书，每本书都有与其关联性很强的书，给一个list<string,string>

代表书和与其关联的书，输出互相关联的最大集合。例如：

三国演义 水浒传

水浒传 红楼梦

哈利波特 时间简史

三国演义，水浒传，红楼梦

the key point here is convert the input list to list of <point, neigbors> , like undirect graph

then BFS to scan the graph and calculate pints of connected graph

/**
 * Created by LEI_D on 6/14/2017.
 */
import java.util.List;
import java.util.LinkedList;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
import java.util.Queue;

public class BookRecomm {


class Item{

    String name;
    String val;
    public Item(String name, String val){
        this.name = name;
        this.val = val;
    }

}

    public List<String> bookRecomm(List<Item> booklist) {
        if (booklist == null || booklist.size() == 0) {
            return new ArrayList<String>();
        }

        Map<String,List<String>> map = new HashMap<String, List<String>>();
        // put undirected graph into map
        for(Item item : booklist) {
            List<String> neigbors = map.get(item.name);
            if (neigbors == null) {
                neigbors = new ArrayList<String>();
                map.put(item.name,neigbors);
            }
            neigbors.add(item.val);

            List<String> neigborsrev = map.get(item.val);
            if (neigborsrev == null) {
                neigborsrev = new ArrayList<String>();
                map.put(item.val,neigborsrev);
            }

            neigborsrev.add(item.name);
        }


        // initial visited map
        Map<String, Boolean> visited = new HashMap<String, Boolean>();
        for(Map.Entry<String,List<String>> entry : map.entrySet()) {
            visited.put(entry.getKey(),false);
        }

        //BFS to find the biggest connected points
        int max = Integer.MIN_VALUE;
        List<String> result = new ArrayList<String>();
        Queue<String> queue = new LinkedList<String>();
        List<String> cur = new ArrayList<String>();

        for(Map.Entry<String,List<String>> entry : map.entrySet()) {
            String bookName = entry.getKey();
            //System.out.println(bookName);
            if (queue.isEmpty()) {
                if (cur.size() > max) {
                    result = new ArrayList<>(cur);
                    max = cur.size();
                }
                cur.clear();
                if(!visited.get(bookName)) {
                    cur.add(bookName);
                    visited.put(bookName,true);
                    List<String> neis = map.get(bookName);
                    for(String nei : neis) {
                        if(!visited.get(nei)) {
                            queue.offer(nei);
                        }
                    }
                }
            }

            while(!queue.isEmpty()) {
                int size = queue.size();
                for(int i = 0; i < size;i++) {
                    bookName = queue.poll();
                    cur.add(bookName);
                    visited.put(bookName,true);
                    for(String str : map.get(bookName)) {
                        if (!visited.get(str)) {
                            queue.offer(str);
                        }
                    }
                }
            }

        }
        return result;
    }
}