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authorJack Sangdahl <[email protected]>2025-03-10 00:36:13 -0600
committerJack Sangdahl <[email protected]>2025-03-10 00:36:13 -0600
commit7c60dee83b436e8e8a667bf9f191beced8de4fc3 (patch)
treeeb7a24ee2067f92245c57bb118e85a1baf15df50 /other/number_atoms.cpp
parent5d7cdc215e4ba1ec4cbb24c084cccb5e5e641468 (diff)
downloadleetcode-7c60dee83b436e8e8a667bf9f191beced8de4fc3.tar.gz
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chore: move cpp and rust code to directory
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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
+}