Expression Add Operation

 1 public class Solution {
 2     public List<String> addOperators(String num, int target) {
 3         List<String> result = new ArrayList<>();
 4         if (num.length() < 2) {
 5             return result;
 6         }
 7         getPath(result, "", num, target, 0, 0L, 0L);
 8         return result;
 9     }
10     
11     private void getPath(List<String> result, String current, String num, int target, int pos, long value, long multi) {
12         if (pos == num.length()) {
13             if (target == value) {
14                 result.add(current);
15             }
16             return;
17         }
18         
19         for (int i = pos; i < num.length(); i++) {
20             if (i != pos && num.charAt(pos) == '0') {
21                 break;
22             }
23             long data = Long.parseLong(num.substring(pos, i + 1));
24             if (pos == 0) {
25                 getPath(result, current + data, num, target, i + 1, data, data);
26             } else {
27                 getPath(result, current + "+" + data, num, target, i + 1, value + data, data);
28                 getPath(result, current + "-" + data, num, target, i + 1, value - data, -data);
29                 getPath(result, current + "*" + data, num, target, i + 1, value - multi + multi * data, multi * data);
30             }
31         }
32     }
33 }

1. Deal with 0 situation : only 0 itself is allowed, it cannot be 04.

2. We have to record the previous value that can be used to extract from previous layer. For example 1234.

You calculate 1 + 2 + 3. Then you want add "*" between 3 and 4. You need to subtract 3 from the 1 + 2 + 3. And mutiple it with 4. So it would be (value - multi + multi * data)

posted on 2016-07-07 12:45 keepshuatishuati 阅读(118) 评论(0) 编辑收藏举报