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-rw-r--r-- | number_atoms.cpp | 75 | ||||
-rw-r--r-- | number_atoms.py | 47 |
2 files changed, 122 insertions, 0 deletions
diff --git a/number_atoms.cpp b/number_atoms.cpp new file mode 100644 index 0000000..2f05d3f --- /dev/null +++ b/number_atoms.cpp @@ -0,0 +1,75 @@ +// 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 +} diff --git a/number_atoms.py b/number_atoms.py new file mode 100644 index 0000000..86fa2d7 --- /dev/null +++ b/number_atoms.py @@ -0,0 +1,47 @@ +# 726. Number of Atoms +from collections import defaultdict + +""" +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(object): + def countOfAtoms(self, formula): + """ + :type formula: str + :rtype: str + """ + dic, coeff, stack, elem, cnt, i = defaultdict(int), 1, [], "", 0, 0 + for c in formula[::-1]: + if c.isdigit(): + cnt += int(c) * (10**i) + i += 1 + elif c == ")": + stack.append(cnt) + coeff *= cnt + i = cnt = 0 + elif c == "(": + coeff //= stack.pop() + i = cnt = 0 + elif c.isupper(): + elem += c + dic[elem[::-1]] += (cnt or 1) * coeff + elem = "" + i = cnt = 0 + elif c.islower(): + elem += c + return "".join(k + str(v > 1 and v or "") for k, v in sorted(dic.items())) + + +if __name__ == "__main__": + obj = Solution() + print(obj.countOfAtoms(formula="H2O")) + print(obj.countOfAtoms(formula="Mg(OH)2")) + print(obj.countOfAtoms(formula="K4(ON(SO3)2)2")) |