1. // "1234" "111" -> "1345"
2. // "9" + "99"
3.  
4.  
5. String sum(String s1, String s2) {
6.   //Do the sum from right to left
7.   int i = s1.length() - 1;
8.   int j = s2.length() - 1;
9.  
10.   int remainder = 0;//0
11.   String output = "";//"2"
12.  
13.   while (i >= 0 || j >= 0) { //i = -1
14.     int c1 = i < 0? 0 : Integer.valueOf(s1.charAt(i));//0
15.     int c2 = j < 0? 0 : Integer.valueOf(s2.charAt(j));//1
16.    
17.     int sum = c1 + c2 + remainder;//2
18.    
19.     if (sum > 9) {
20.       sum = sum - 10;
21.       remainder = 1;
22.     } else {
23.       remainder = 0;
24.     }
25.     output = sum + output;
26.    
27.     i --;
28.     j --;
29.   }
30.  
31.   if (remainder > 0) {
32.     output = remainder + output;
33.   }
34.  
35.   return output;
36. }
37.  
38. // ["alaska", "alabama", "jake"]
39. // ala
40. // alaska, alabama
41.  
42. TrieNode {
43.  
44.   HashMap<Character, TrieNode> children;
45. }
46.  
47. TrieNode buildTrie(List<String> dictionary) {
48.   TrieNode node = new TrieNode();
49.   for (String s : dictionary) {
50.     TrieNode current = node;
51.     for (int i = 0; i < s.length() - 1; i ++) {
52.       char c =  s.charAt(i);
53.       TrieNode child = children.get();
54.      
55.       if (child == null) {
56.         TrieNode newNode = new TrieNode();
57.         children.put(c, newNode);
58.         current = newNode;
59.       } else {
60.         current = child;
61.       }
62.     }
63.   }
64.   return node;
65. }
66.  
67. List<String> searchFromTrie(TrieNode root, String prefix) {
68.   TrieNode current = root;
69.   for (int i = 0; i < prefix.length() - 1; i ++) {
70.     char c = prefix.charAt(i);
71.    
72.     TrieNode child = current.children.get(c);
73.     if (child != null) {
74.       current = child;
75.     } else {
76.       return new ArrayList<>();
77.     }
78.   }
79.  
80.  
81. }
82.  
83.  
84.  
85.  
86.  
87.  
88.