Create Solution.java

Author: yanglbme

solution/0700-0799/0726.Number of Atoms/Solution.java

@@ -0,0 +1,43 @@
+class Solution {
+    public String countOfAtoms(String formula) {
+        Map<String, Integer> map = new HashMap<>();
+        int[] stack = new int[1000];
+        int top = 0, multiplier = 1, freq = 0;
+        char[] c = formula.toCharArray();
+        for (int i = c.length - 1; i >= 0; i--) {
+            if (c[i] >= 'a' && c[i] <= 'z') {
+                int end = i--;
+                while (i >= 0 && c[i] >= 'a' && c[i] <= 'z') i--;
+                String key = new String(c, i, end - i + 1);
+                map.put(key, map.getOrDefault(key, 0) + Math.max(freq, 1) * multiplier);
+                freq = 0;
+            } else if (c[i] >= 'A' && c[i] <= 'Z') {
+                String key = new String(c, i, 1);
+                map.put(key, map.getOrDefault(key, 0) + Math.max(freq, 1) * multiplier);
+                freq = 0;
+            } else if (c[i] >= '0' && c[i] <= '9') {
+                freq = c[i] - '0';
+                int p = 10;
+                while (i - 1 >= 0 && c[i - 1] >= '0' && c[i - 1] <= '9') {
+                    freq += p * (c[--i] - '0');
+                    p *= 10;
+                }
+            } else if (c[i] == ')') {
+                stack[top++] = multiplier;
+                multiplier *= Math.max(freq, 1);
+                freq = 0;
+            } else {
+                multiplier = stack[--top];
+            }
+        }
+        List<String> keys = new ArrayList<>(map.keySet());
+        Collections.sort(keys);
+        StringBuilder sb = new StringBuilder();
+        for (String key : keys) {
+            sb.append(key);
+            int f = map.get(key);
+            if (f > 1) sb.append(f);
+        }
+        return sb.toString();
+    }
+}