algo-aha

分数转成循环小数

• https://leetcode.com/problems/fraction-to-recurring-decimal/

string fractionToDecimal(int numerator, int denominator) {
    if (denominator == 0) return "NAN";
    if (numerator == 0) return "0";

    string ans;
    bool neg = (numerator ^ denominator) < 0;
    if (neg) ans += "-";

    long n = labs(numerator), d = labs(denominator);
    ans += to_string(n / d);

    long rmd = n % d;
    if (rmd > 0) ans += ".";

    // 为插入循环节的左括号，记录 余数=>对应左括号应在ans串的位置
    unordered_map<long, int> mp;
    while (rmd) {
        if (mp.count(rmd)) { // 找到循环节
            ans.insert(mp[rmd], "(");
            ans += ")";
            return ans;
        }

        mp[rmd] = ans.size();
        rmd *= 10;
        ans += to_string(rmd / d);
        rmd %= d;
    }
    return ans;
}