Reverse Only Letters

Given a string s, reverse the string according to the following rules:

All the characters that are not English letters remain in the same position.
All the English letters (lowercase or uppercase) should be reversed.
Return s after reversing it.

Example 1:

Input: s = "ab-cd"
Output: "dc-ba"
Example 2:

Input: s = "a-bC-dEf-ghIj"
Output: "j-Ih-gfE-dCba"
Example 3:

Input: s = "Test1ng-Leet=code-Q!"
Output: "Qedo1ct-eeLg=ntse-T!"
Constraints:

1 <= s.length <= 100
s consists of characters with ASCII values in the range [33, 122].
s does not contain '\"' or '\\'.
 

思路一：雙指標，先定位兩個指標的位置，然後交換合法的字元

public String reverseOnlyLetters(String s) {
    char[] chars = s.toCharArray();

    int i = 0;
    int j = chars.length - 1;

    while (true) {
        while (i < chars.length && !Character.isLetter(chars[i])) {
            i++;
        }
        while (j >= 0 && !Character.isLetter(chars[j])) {
            j--;
        }

        if (i < j) {
            char t = chars[i];
            chars[i] = chars[j];
            chars[j] = t;
        } else {
            break;
        }
        i++;
        j--;
    }

    return new String(chars);
}