++array[s.charAt(i) - 'A'] 到底是做什么的?

2022-01-12 00:00:00 string arrays char java

for (int i = 0; i < s.length(); ++i) 
    {
        if (s.charAt(i) >= 'A' && s.charAt(i) <= 'Z') 
        {
            ++array[s.charAt(i) - 'A'];
        }
    }

我了解 For 循环.s.length() 是 26，确切地说是 int[26].所以这个循环会发生26次，0-25.如果 i, 0-25 处的字符介于 AZ 之间或为 AZ 它将继续执行 ++array[s.charAt(i) - 'A']; 从我看到的情况来看，它会添加一次数组每个循环，或者每次循环添加一次数组的值，对于 char i 处的字符串，所以第一个是 0 秒是 2，因为数组从 0 开始.所以在 i 的位置添加一个数组 -'A' 是我感到困惑的地方.

I understand the For loop. the s.length() is 26, int[26] to be exact. so this loop will occur 26 times, 0-25. If the Char at i, 0-25 is between or are A-Z it will then proceed to ++array[s.charAt(i) - 'A']; From what i see it adds array once per loop, or adds the value of array once per loop, for the String at char i so the first one would be 0 second would be 2, because arrays start at 0. so adding an array at location of i -'A' is where i get confused.

推荐答案

语句 ++array[s.charAt(i) - 'A']; 正在递增索引数组中的值通过 s.charAt(i) - 'A'.

The statement ++array[s.charAt(i) - 'A']; is incrementing the value in the array indexed by s.charAt(i) - 'A'.

这个循环的作用是计算 s 中每个字母出现的次数.

What this loop does is that it counts up the number of occurrences of each letter in s.

- 'A' 的原因是它移动"了 ascii/unicode 值，因此 A - Z 的值是 0 - 25.因此更适合作为数组索引.

The reason for - 'A', is that it "shifts" the ascii/unicode value so that A - Z have values 0 - 25. And are thus more suitable as an array index.

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