[LeetCode] Fraction to Recurring Decimal 哈希表

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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 Hash Table Math

 

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　　题目其实挺容易的，需要考虑的是溢出问题，long int 长度是32 位的， long long int 才是64位。

 

#include <iostream>
#include <unordered_map>
#include <string>
#include <sstream>
using namespace std;

class Solution {
public:
    string fractionToDecimal(int numerator, int denominator) {
        bool flag1 = numerator<0;
        bool flag2 = denominator<0;
        unsigned numer = flag1?-numerator:numerator;
        unsigned denom = flag2?-denominator:denominator;

        if(denom==0)  return "";
        if(numer==0)    return "0";
        stringstream ss;
        ss<<numer/denom;
        string ret = ss.str();
        unsigned long long int lft = numer%denom;

        unordered_map<unsigned int,unsigned int> mp;
        string ret1="";
        unsigned int cnt = 1;
        while(lft){
            if(mp[lft]==0){
                mp[lft]=cnt++;
                ret1 += (lft*10)/denom + '0';
                lft = (lft*10)%denom;
                continue;
            }
            ret1 = ret1.substr(0,mp[lft]-1) + "(" + ret1.substr(mp[lft]-1) + ")";
            break;
        }
        if(ret1 != "")    ret += "." + ret1;
        if(flag1^flag2) ret = "-" + ret;
        return ret;
    }
};

int main()
{
    Solution sol;
    cout<<sol.fractionToDecimal(-1,-2147483648)<<endl;
    return 0;
}