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592.cpp
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592.cpp
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class Solution {
public:
int getLsm(int a, int b) {
return a * b / __gcd(a, b);
}
pair<int, int> parseFraction(string& fraction) {
int currentNumerator = -1;
int currentDenominator = -1;
string token;
stringstream ss(fraction);
while (getline(ss, token, '/')) {
if (currentNumerator == -1) currentNumerator = stoi(token);
else currentDenominator = stoi(token);
}
return make_pair(currentNumerator, currentDenominator);
}
pair<int, int> add(pair<int, int>& prev, pair<int, int>& next) {
if (prev.second == -1) return next;
int prevNumerator = prev.first;
int prevDenominator = prev.second;
int nextNumerator = next.first;
int nextDenominator = next.second;
int lsm = getLsm(prevDenominator, nextDenominator);
int prevNumeratorLsm = prevNumerator * lsm / prevDenominator;
int nextNumeratorLsm = nextNumerator * lsm / nextDenominator;
int numeratorLsm = prevNumeratorLsm + nextNumeratorLsm;
return {numeratorLsm, lsm};
}
void reduce(pair<int, int>& fraction) {
int gcd = __gcd(abs(fraction.first), fraction.second);
fraction.first = fraction.first / gcd;
fraction.second = fraction.second / gcd;
}
string fractionAddition(string expression) {
if (expression[0] != '-') expression = "+" + expression;
vector<string> fractions;
pair<int, int> current = {-1, -1};
int index = 0;
int n = expression.size();
while (index < n) {
if (expression[index] == '+') {
index++;
int start = index;
while (index + 1< n && expression[index + 1] != '+' && expression[index + 1] != '-') {
index++;
}
// [start, index]
string fraction = expression.substr(start, index - start + 1);
pair<int, int> fractionNums = parseFraction(fraction);
current = add(current, fractionNums);
index++;
}
else {
index++;
int start = index;
while (index + 1< n && expression[index + 1] != '+' && expression[index + 1] != '-') {
index++;
}
// [start, index]
string fraction = expression.substr(start, index - start + 1);
pair<int, int> fractionNums = parseFraction(fraction);
fractionNums.first = -fractionNums.first;
current = add(current, fractionNums);
index++;
}
}
if (current.first == 0) return "0/1";
reduce(current);
string res;
res += to_string(current.first);
res += "/";
res += to_string(current.second);
return res;
}
};