leetcode之字符串一: 查找共用字符

原题:

力扣https://leetcode-cn.com/problems/find-common-characters/submissions/

给你一个字符串数组 words ，请你找出所有在 words 的每个字符串中都出现的共用字符（ 包括重复字符），并以数组形式返回。你可以按 任意顺序 返回答案。
 

示例 1：

输入：words = ["bella","label","roller"]
输出：["e","l","l"]

示例 2：

输入：words = ["cool","lock","cook"]
输出：["c","o"]
 

提示：

1 <= words.length <= 1001 <= words[i].length <= 100words[i] 由小写英文字母组成

package com.leetcode.string;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class Solution11 {
    public static void main(String[] args) {
        String[] words = {"cool","lock","cook"};
        System.out.println(commonChars(words));
    }


    public static List commonChars(String[] words) {
        List> list = new ArrayList>();

        for (String word:words) {
            HashMap map = new HashMap();
            for (int i = 0; i < word.length(); i++) {
                char c = word.charAt(i);
                if (map.containsKey(c)) {
                    map.put(c, map.get(c) + 1);
                } else {
                    map.put(c, 1);
                }
            }
            list.add(map);
        }

        ArrayList l = new ArrayList();
        for (char c = 'a'; c <= 'z'; c++){
            int min = 0;        // 找最少出现的次数
            int count2 = 0;
            for (HashMap map:list) {
                Integer count = map.get(c);
                if (count == null) {
                    min = 0;
                    count2++;
                    break;
                }
                if (count2 == 0) {
                    min = count;
                }
                min = Math.min(min, count);
                count2++;
            }
            for (int i = 0; i < min; i++) {
                l.add(c + "");
            }
        }

        return l;
    }
}