Leetcode-Fraction to Recurring Decimal

LiBlog發表於2014-12-17
LeetCodeFractionDecimal

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

For example,

  • Given numerator = 1, denominator = 2, return "0.5".
  • Given numerator = 2, denominator = 1, return "2".
  • Given numerator = 2, denominator = 3, return "0.(6)".

Analysis:

We need to use long type.

Solution:

Store every digit in float part, and assemble the string at last.

 1 public class Solution {
 2     public String fractionToDecimal(int numerator, int denominator) {
 3         if (denominator==0) return "";
 4         if (numerator==0) return "0";
 5         boolean neg = false;
 6         if (numerator>0){
 7             numerator = -numerator;
 8             neg = !neg;
 9         }
10 
11         if (denominator>0){
12             denominator = -denominator;
13             neg = !neg;
14         }
15  
16 
17         long intPart = (long) numerator/ (long) denominator;
18         long left = numerator%denominator;
19 
20         List<Integer> digitList = new ArrayList<Integer>();
21         List<Long> leftList = new ArrayList<Long>();
22         int iterStart = -1;
23         while (left!=0){
24             int digit = (int) (left*10/denominator);
25             digitList.add(digit);
26             leftList.add(left);
27             long newLeft = (left*10)%denominator;
28             if (leftList.contains(newLeft)){
29                 iterStart = leftList.indexOf(newLeft);
30                 break;
31             }
32             left = newLeft;
33         }
34 
35         //Assemble the string.
36         StringBuilder builder = new StringBuilder();
37         if (neg) builder.append('-');
38         builder.append(intPart);
39 
40         if (digitList.size()==0) return builder.toString();
41         else {
42             builder.append('.');
43             if (iterStart==-1)
44                 for (int i=0;i<digitList.size();i++)
45                     builder.append(digitList.get(i));
46             else {
47                 //append non-iter part.
48                 for (int i=0;i<iterStart;i++)
49                     builder.append(digitList.get(i));
50                 builder.append('(');
51                 //append iter part.
52                 for (int i=iterStart;i<digitList.size();i++)
53                     builder.append(digitList.get(i));
54                 builder.append(')');
55             }
56             return builder.toString();
57        }        
58         
59     }
60 }

Solution 2:

Store the postion of the corresponding left of every digit, assemble the result string in place.

 1 public class Solution {
 2     public String fractionToDecimal(long numerator, long denominator) {
 3         if (denominator==0) return "";
 4         if (numerator==0) return "0";
 5         String res = "";
 6         if (numerator<0 ^ denominator<0)
 7             res = "-";         
 8  
 9         numerator = Math.abs(numerator);
10         denominator = Math.abs(denominator);
11 
12         long intPart = numerator/denominator;
13         long left = numerator%denominator;
14         res = res.concat(Long.toString(intPart));
15         Map<Long,Integer> posMap = new HashMap<Long,Integer>();
16         if (left!=0) res = res.concat(".");
17         while (left!=0){
18             long digit = left*10/denominator;
19             posMap.put(left,res.length());
20             res = res.concat(Long.toString(digit));
21             left = left*10%denominator;
22             if (posMap.containsKey(left)){
23                 int pos = posMap.get(left);
24                 res = res.substring(0,pos)+"("+res.substring(pos,res.length())+")";
25                 left = 0;
26             }
27         }            
28 
29         return res;        
30         
31     }
32 }

 

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