From 7c60dee83b436e8e8a667bf9f191beced8de4fc3 Mon Sep 17 00:00:00 2001 From: Jack Sangdahl Date: Mon, 10 Mar 2025 00:36:13 -0600 Subject: chore: move cpp and rust code to directory --- other/number_atoms.cpp | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 other/number_atoms.cpp (limited to 'other/number_atoms.cpp') diff --git a/other/number_atoms.cpp b/other/number_atoms.cpp new file mode 100644 index 0000000..2f05d3f --- /dev/null +++ b/other/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 cnts = parse_formula(formula, i); + for (pair p : cnts) { + ans += p.first; + if (p.second > 1) + ans += to_string(p.second); + } + return ans; + } + +private: + map parse_formula(string &s, int &i) { + map cnts; + const int n = s.size(); + while (i < n && s[i] != ')') { + map cnt = parse_unit(s, i); + merge(cnts, cnt, 1); + } + return cnts; + } + map parse_unit(string &s, int &i) { + map cnts; + const int n = s.size(); + if (s[i] == '(') { + map 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 &cnts, map &cnt, int times) { + for (pair 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 +} -- cgit v1.2.3