Skip to content

halfrost/LeetCode-Go

Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
..
Failed to load latest commit information.
726. Number of Atoms.go
726. Number of Atoms_test.go
README.md

726. Number of Atoms

题目

Given a chemical `formula` (given as a string), return the count of each atom.

An atomic element always starts with an uppercase character, then zero or more lowercase letters, representing the name.

1 or more digits representing the count of that element may follow if the count is greater than 1. If the count is 1, no digits will follow. For example, H2O and H2O2 are possible, but H1O2 is impossible.

Two formulas concatenated together produce another formula. For example, H2O2He3Mg4 is also a formula.

A formula placed in parentheses, and a count (optionally added) is also a formula. For example, (H2O2) and (H2O2)3 are formulas.

Given a formula, output the count of all elements as a string in the following form: the first name (in sorted order), followed by its count (if that count is more than 1), followed by the second name (in sorted order), followed by its count (if that count is more than 1), and so on.

Example 1:

``````Input:
formula = "H2O"
Output: "H2O"
Explanation:
The count of elements are {'H': 2, 'O': 1}.
``````

Example 2:

``````Input:
formula = "Mg(OH)2"
Output: "H2MgO2"
Explanation:
The count of elements are {'H': 2, 'Mg': 1, 'O': 2}.
``````

Example 3:

``````Input:
formula = "K4(ON(SO3)2)2"
Output: "K4N2O14S4"
Explanation:
The count of elements are {'K': 4, 'N': 2, 'O': 14, 'S': 4}.
``````

Note:

• All atom names consist of lowercase letters, except for the first character which is uppercase.
• The length of `formula` will be in the range `[1, 1000]`.
• `formula` will only consist of letters, digits, and round parentheses, and is a valid formula as defined in the problem.

解题思路

• 利用栈处理每个化学元素，用 map 记录每个化学元素的个数，最终排序以后输出即可
• 注意化学元素有些并不是单一字母，比如镁元素是 Mg，所以需要考虑字母的大小写问题。
You can’t perform that action at this time.