https://leetcode.com/problems/evaluate-division/public class Solution {    private Map mp;    private class Item {        public String str;        public double prop;        public Item(String s, double p) {            str = s;            prop = p;        }    }        public double[] calcEquation(String[][] equations, double[] values, String[][] queries) {        mp = new HashMap();                for (int i=0; i<values.length; i++) {            String str1 = equations[i][0];             String str2 = equations[i][1];            double val = values[i];                        List lt = (List)mp.remove(str2);            if (lt == null) {                lt = new ArrayList();            }            Item itm = new Item(str1, val);            lt.add(itm);            mp.put(str2, lt);                        lt = (List)mp.remove(str1);            if (lt == null) {                lt = new ArrayList();            }            itm = new Item(str2, 1/val);            lt.add(itm);            mp.put(str1, lt);        }                double []ret = new double[queries.length];        Set st = new HashSet();        Queue qe = new LinkedList();                Iterator itr;        List lt;        Item baseItm;                for (int i=0; i<queries.length; i++) {            st.clear();            qe.clear();                        double dret = -1;            String str1 = queries[i][0];            String str2 = queries[i][1];                        qe.offer(new Item(str2, 1));            st.add(str2);                        while ((baseItm = (Item)qe.poll()) != null) {                                lt = (List)mp.get(baseItm.str);                if (lt == null) {                    continue;                }                                itr = lt.iterator();                                while (itr.hasNext()) {                                        Item itmm = (Item)itr.next();                    if (itmm.str.equals(str1)) {                        dret = itmm.prop * baseItm.prop;                        break;                    }                                        if (st.contains(itmm.str)) {                        continue;                    }                    Item newItm = new Item(itmm.str, itmm.prop*baseItm.prop);                    qe.offer(newItm);                    st.add(itmm.str);                }                                if (dret != -1) {                    break;                }            }                        ret[i] = dret;        }                return ret;            }}