evaluate-division

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;
        
    }
}