https://leetcode.com/problems/number-of-atoms

hard/number_of_atoms.py

@@ -0,0 +1,40 @@
+# https://leetcode.com/problems/number-of-atoms
+from typing import Dict, List
+
+class Solution:
+    def countOfAtoms(self, formula: str) -> str:
+        s: List[Dict[str, int]] = [{}]
+        idx = 0
+        while idx < len(formula):
+            if formula[idx] == ')':
+                idx += 1
+                mul = 0
+                while idx < len(formula) and formula[idx].isdecimal():
+                    mul = mul * 10 + int(formula[idx])
+                    idx += 1
+                if mul == 0:
+                    mul = 1
+                d = s.pop()
+                for key in d:
+                    s[-1][key] = s[-1].get(key, 0) + (d[key] * mul)
+                continue
+            if formula[idx] == '(':
+                s.append({})
+                idx += 1
+                continue
+            key = ''
+            if formula[idx].isalpha():
+                key += formula[idx]
+                idx += 1
+                while idx < len(formula) and formula[idx].islower():
+                    key += formula[idx]
+                    idx += 1
+            cnt = 0
+            while idx < len(formula) and formula[idx].isdecimal():
+                cnt = cnt * 10 + int(formula[idx])
+                idx += 1
+            if cnt == 0:
+                cnt = 1
+            s[-1][key] = s[-1].get(key, 0) + cnt
+        return ''.join(key + (str(v) if v > 1 else '') for key, v in sorted(s[-1].items()))
+