LeetCode知识点总结 - 1002

Given a string array words, return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order.

需要两个helper function：
1 计算每个string里面出现的字母次数
2 求两个string里面字母的交集（取两个次数之间小的）
最后把每个次数大于0的字母按剩余次数加到array中返回。

class Solution {
    public List commonChars(String[] words) {
         int[] last = count(words[0]);
        for (int i = 1; i < words.length; i++) {
            last = intersection(last, count(words[i]));
        }
        List arr = new ArrayList<>();
        for (int i = 0; i < 26; i++) {
            if (last[i] != 0) {
                char a = 'a';
                a += i;
                String s = String.valueOf(a);
                while (last[i] > 0) {
                    arr.add(s);
                    last[i]--;
                }
            }
        }
        return arr;
    }

    int[] intersection(int[] a, int[] b) {
        int[] t = new int[26];
        for (int i = 0; i < 26; i++) {
            t[i] = Math.min(a[i], b[i]);
        }
        return t;
    }

    int[] count(String str) {
        int[] t = new int[26];
        for (char c : str.toCharArray()) t[c - 'a']++;
        return t;
    }
}