3412. 计算字符串的镜像分数

方法一：26个栈

stacks[25 - c]即可找出存放当前字符的镜像字符的栈

class Solution {
    public long calculateScore(String s) {
        Deque<Integer>[] stacks = new Deque[26];
        Arrays.setAll(stacks, i -> new ArrayDeque<>());
        long res = 0;
        for (int i = 0; i < s.length(); ++i) {
            int c = s.charAt(i) - 'a';
            if (!stacks[25 - c].isEmpty())
                res += i - stacks[25 - c].pop();
            else
                stacks[c].push(i);
        }
        return res;
    }
}