166 Fraction to Recurring Decimal

链接：https://leetcode.com/problems/fraction-to-recurring-decimal/
问题描述：
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)”.
Credits:
Special thanks to @Shangrila for adding this problem and creating all test cases.

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这个问题很容易理解，两数相除，如果有陷入循环，则用（）将循环部分括起来。这题问题出在例子实在太极端，出题人真是丧心病狂，写C写的吐血了，以后都用C++吧，STL确实提供了丰富好用的功能，C实在玩不起了。C代码：

struct data{   long long int val;   int remain;   int pos;   struct data *next;};int calcintlength(long long int num){  int result=0;   if(num==0)       return 1;   while(num>0)   {     result++;     num/=10;   }   return result;}char* fractionToDecimal(int numerator, int denominator) {    long long int      mnumerator=numerator,mdenominator=denominator,intger=0;    int intlength=0,totallength=0,fractionlength=0,pos=0;    struct data head,*cur,*a;    char* result;    char flag=0;        if(mnumerator==0)    {        result=(char*)malloc(2);        result[0]='0';        result[1]='\0';        return result;    }    if((mnumerator<0&&mdenominator>0)||(mnumerator>0&&mdenominator<0))        flag=1;    mdenominator=mdenominator>0? mdenominator:-mdenominator;    mnumerator=mnumerator>0?mnumerator:-mnumerator;    head.next=NULL;    cur=&head;    intger=mnumerator/mdenominator;    mnumerator%=mdenominator;    fractionlength=-1;    while(mnumerator!=0)    {      a=(struct data *)malloc(sizeof(struct data));      a->next=NULL;      a->val=mnumerator/mdenominator;      mnumerator=mnumerator%mdenominator;      a->remain=mnumerator;      a->pos=++fractionlength;      cur->next=a;      cur=head.next;      while(cur!=a)      {          if(cur->remain==mnumerator)          {          pos=cur->pos;          goto deal;          }          cur=cur->next;      }      mnumerator*=10;    }deal:    intlength=calcintlength(intger);    totallength+=intlength;    //只有整数，没有小数    if(fractionlength<=0)    {        int i=0;        result=(char *)malloc(totallength+1);        result[totallength]='\0';        for(;i<totallength;i++)        {         result[totallength-i-1]=intger%10+'0';         intger/=10;        }        goto end;    }    a=head.next;    head=*head.next;    cur=head.next;    free(a);    //有小数，没循环    totallength++;    if(mnumerator==0)    {        int i=0;        totallength+=fractionlength;        result=(char *)malloc(totallength+1);        result[totallength]='\0';        for(;i<intlength;i++)        {         result[intlength-i-1]=intger%10+'0';         intger/=10;        }        result[intlength++]='.';        while(cur!=NULL)        {               result[intlength++]=cur->val+'0';          a=cur;          cur=cur->next;          free(a);        }        goto end;    }    //这里处理有循环    else    {        int i=0;        totallength+=2;        totallength+=fractionlength;        result=(char *)malloc(totallength+1);        result[totallength]='\0';        result[totallength-1]=')';        for(;i<intlength;i++)        {         result[intlength-i-1]=intger%10+'0';         intger/=10;        }        result[intlength++]='.';        result[intlength+pos]='(';        for( i=0;i<fractionlength+1;i++,intlength++)        {         if(i==pos)             continue;         else         {           result[intlength]=cur->val+'0';                  a=cur;          cur=cur->next;          free(a);;         }         }        goto end;    }end:    if(flag==1)    {      char *r=(char *)malloc(totallength+2);      memcpy(r+1,result,totallength+1);      r[0]='-';      free(result);      result=r;    }    return result;}

相比之下使用STL的C++代码不经短小了许多，也更容易读懂。

class Solution {public:  string fractionToDecimal(int numerator, int denominator)   {     long long int mnumerator=numerator,mdenominator=denominator;     if(numerator==0) return "0";     string result;      if((mnumerator<0&&mdenominator>0)||(mnumerator>0&&mdenominator<0)) result+='-';      mnumerator= mnumerator>0? mnumerator:-mnumerator;      mdenominator= mdenominator>0? mdenominator:-mdenominator;      result+=to_string(mnumerator/mdenominator);      mnumerator%=mdenominator;      if(mnumerator==0)          return result;      result+='.';      map<int,int> map;      while(mnumerator!=0)      {         if(map.find(mnumerator)!=map.end())             return result.substr(0,map[mnumerator])+"("+result.substr(map[mnumerator],result.size())+')';       map[mnumerator]=result.size();         mnumerator*=10;      result+=to_string(mnumerator/mdenominator);      mnumerator=mnumerator%mdenominator;      }      return result;  }};