[每日 LeetCode] 1002. Find Common Characters

Description:

Given an array A of strings made only from lowercase letters, return a list of all characters that show up in all strings within the list (including duplicates) .  For example, if a character occurs 3 times in all strings but not 4 times, you need to include that character three times in the final answer.

You may return the answer in any order.

Example 1:

Input: ["bella","label","roller"]
Output: ["e","l","l"]

Example 2:

Input: ["cool","lock","cook"]
Output: ["c","o"]

Note:

1. 1 <= A.length <= 100
2. 1 <= A[i].length <= 100
3. A[i][j] is a lowercase letter

思路：本文求二维字符串数组中每组字符中的重复字符。考虑维护一个长度为 26 的数组，对每个串进行扫描，保证每次存储的是已经比较过的公共字符。其中 count_min 数组来保存每个字符在其所属字符串中出现的最小次数， count 数组来保存每个字符在每一种字符串中出现的最小次数。

C++ 代码

class Solution
{
  public:
	vector<string> commonChars(vector<string> &A)
	{
		vector<string> res;
		vector<int> count(26, INT_MAX);
		for (auto a : A)
		{
			vector<int> count_min(26, 0);
			for (auto c : a)
				++count_min[c - 'a'];
			for (int i = 0; i < 26; i++)
				count[i] = min(count_min[i], count[i]);
		}
		for (int i = 0; i < 26; i++)
		{
			for (int j = 0; j < count[i]; j++)
			{
				res.push_back(string(1, i + 'a'));
			}
		}
		return res;
	}

运行时间：12ms

运行内存：10M