[LeetCode] Reverse Words in a String III 翻轉字符串中的單詞之三

 

Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

 

Note: In the string, each word is separated by single space and there will not be any extra space in the string.

 

這道題讓我們翻轉字符串中的每個單詞，感覺整體難度要比之前兩道Reverse Words in a String II和Reverse Words in a String要小一些，由於題目中說明了沒有多余空格，使得難度進一步的降低了。首先我們來看使用字符流處理類stringstream來做的方法，相當簡單，就是按順序讀入每個單詞進行翻轉即可，參見代碼如下：

 

解法一：

class Solution {
public:
    string reverseWords(string s) {
        string res = "", t = "";
        istringstream is(s);
        while (is >> t) {
            reverse(t.begin(), t.end());
            res += t + " ";
        }
        res.pop_back();
        return res;
    }
};

 

下面我們來看不使用字符流處理類，也不使用STL內置的reverse函數的方法，那么就是用兩個指針，分別指向每個單詞的開頭和結尾位置，確定了單詞的首尾位置后，再用兩個指針對單詞進行首尾交換即可，有點像驗證回文字符串的方法，參見代碼如下：

 

解法二：

class Solution {
public:
    string reverseWords(string s) {
        int start = 0, end = 0, n = s.size();
        while (start < n && end < n) {
            while (end < n && s[end] != ' ') ++end;
            for (int i = start, j = end - 1; i < j; ++i, --j) {
                swap(s[i], s[j]);
            }
            start = ++end;
        }
        return s;
    }
};

 

類似題目：

Reverse Words in a String II

Reverse Words in a String

 

參考資料：

https://discuss.leetcode.com/topic/85773/nothing-fancy-straight-java-stringbuilder

https://discuss.leetcode.com/topic/85797/java-two-methods-3-line-using-built-in-and-char-array

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