917.reverse-only-letters.cpp

/*
 * @lc app=leetcode id=917 lang=cpp
 *
 * [917] Reverse Only Letters
 *
 * https://leetcode.com/problems/reverse-only-letters/description/
 *
 * algorithms
 * Easy (56.15%)
 * Likes:    279
 * Dislikes: 27
 * Total Accepted:    30.9K
 * Total Submissions: 55.1K
 * Testcase Example:  '"ab-cd"'
 *
 * Given a string S, return the "reversed" string where all characters that are
 * not a letter stay in the same place, and all letters reverse their
 * positions.
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 * Example 1:
 * 
 * 
 * Input: "ab-cd"
 * Output: "dc-ba"
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 * Example 2:
 * 
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 * Input: "a-bC-dEf-ghIj"
 * Output: "j-Ih-gfE-dCba"
 * 
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 * Example 3:
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 * Input: "Test1ng-Leet=code-Q!"
 * Output: "Qedo1ct-eeLg=ntse-T!"
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 * Note:
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 * S.length <= 100
 * 33 <= S[i].ASCIIcode <= 122 
 * S doesn't contain \ or "
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 */
class Solution {
public:
    string reverseOnlyLetters(string S) {
        int l = 0, r = S.size() - 1;
        while (l < r) {
            if (isLetter(S[l]) && isLetter(S[r])) {
                swap(S[l], S[r]);
                l++;r--;
            } else if (!isLetter(S[l]))
                l++;
            else if (!isLetter(S[r]))
                r--;
        }
        return S;
    }
    
    bool isLetter(char c) {
        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
    }
};