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// 726. Number of Atoms
#include "leetcode.h"
/*
* given a string 'formula' representing a chemical formula, return the count of
* each atom. the atomic element always stats with an uppercase character, then
* zer or more lowercase letters, representing the name. one or more digits
* representing that element's count may follow if the count is greater than 1.
* if the count is 1, no digits will follow. return the count of all elements as
* a string in the following form: the first name, followed by its count,
* followed by the second name, followed by its count, and so on.
*/
class Solution {
public:
string countOfAtoms(string formula) {
string ans;
const int n = formula.size();
int i = 0;
map<string, int> cnts = parse_formula(formula, i);
for (pair<string, int> p : cnts) {
ans += p.first;
if (p.second > 1)
ans += to_string(p.second);
}
return ans;
}
private:
map<string, int> parse_formula(string &s, int &i) {
map<string, int> cnts;
const int n = s.size();
while (i < n && s[i] != ')') {
map<string, int> cnt = parse_unit(s, i);
merge(cnts, cnt, 1);
}
return cnts;
}
map<string, int> parse_unit(string &s, int &i) {
map<string, int> cnts;
const int n = s.size();
if (s[i] == '(') {
map<string, int> cnt = parse_formula(s, ++i);
int digits = parse_digits(s, ++i);
merge(cnts, cnt, digits);
} else {
int i0 = i++;
while (i < n && islower(s[i]))
i++;
string atom = s.substr(i0, i - i0);
int digits = parse_digits(s, i);
cnts[atom] += digits;
}
return cnts;
}
int parse_digits(string &s, int &i) {
int i0 = i;
while (i < s.size() && isdigit(s[i]))
i++;
int digits = i == i0 ? 1 : stoi(s.substr(i0, i - i0));
return digits;
}
void merge(map<string, int> &cnts, map<string, int> &cnt, int times) {
for (pair<string, int> p : cnt)
cnts[p.first] += p.second * times;
}
};
int main() {
Solution obj;
char f1[] = "H2O", f2[] = "Mg(OH)2", f3[] = "K4(ON(SO3)2)2";
cout << obj.countOfAtoms(f1) << endl; // expect: H2O
cout << obj.countOfAtoms(f2) << endl; // expect: H2MgO2
cout << obj.countOfAtoms(f3) << endl; // expect: K4N2O14S4
}
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