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String manipulation is an essential skill in programming, as it helps us process and analyze text data efficiently. C++ provides a rich set of string manipulation functions and objects, making it easier to work with text data.

In this article, we will discuss how to reverse a string according to the number of words in C++.

方法

Approach 1 − Using stringstreams and vectors

方法2 - 使用子字符串和字符串操作函数

Syntax

在C++中的字符串对象：std::string类是C++标准库的一部分，提供了各种字符串操作函数。

String manipulation functions: Some common string manipulation functions in C++ include length(), substr(), find(), erase(), and replace().

std::string reverseStringByWords(const std::string& input) {}
std::reverse(words.begin(), words.end());

Approach 1:- Using stringstreams and vectors

This approach employed in the code involves converting the input string into a sequence of words using a stringstream object. The words are then extracted one by one from the stream and stored in a collection of strings represented by a vector.

Subsequently, the collection of words is reversed using the reverse function from the algorithm library. The reversed words are then joined together to form the final output string, with a space appended after each word except the last one.

算法

• 开始

• 获取输入字符串。

• 从输入字符串创建一个stringstream。

• 初始化一个空向量来存储单词。

• 通过stringstream迭代提取单词。

• Extract a word from the stringstream.

• Push the extracted word into the vector.

• Reverse the vector containing the words.

• 初始化一个空的输出字符串。

• 通过反向遍历向量形成输出字符串。

• Add each word from the reversed vector to the output string, followed by a space.

• Remove the last space from the output string.

• 返回输出字符串。

• End

Example

The code embodies a procedure that inverts the sequence of words in a specified string. This is accomplished by first transforming the input string into a word-based stream through utilization of a stringstream object. Subsequently, the words are extracted one at a time and placed into a vector. Then, the reverse function from the algorithm library is employed to reverse the vector. Finally, the inverted words are joined together to form the conclusive output string, with spaces inserted after each word, excluding the final one. The last space is then deleted from the output string, rendering a compact and comprehensible solution that makes the most of Standard Library features like stringstreams, vectors, and the algorithm library.

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <algorithm>

std::string reverseStringByWords(const std::string& input) {
   std::stringstream ss(input);
   std::string word;
   std::vector<std::string> words;

   while (ss >> word) {
      words.push_back(word);
   }

   std::reverse(words.begin(), words.end());

   std::string output;
   for (const auto& w : words) {
      output += w + " ";
   }

   output.pop_back(); // Remove the last space
   return output;
}

int main() {
   std::string input = "Hello, how are you?";
   std::string output = reverseStringByWords(input);
   std::cout << "Input: " << input << std :: endl;
   std:: cout << "Output: " << output << std :: endl;
   return 0;
}

Output

的中文翻译为：

输出

Input: Hello, how are you?
Output: you? are how Hello,

方法2：使用子字符串和字符串操作函数

方法2是将字符串中的单词顺序颠倒的另一种解决方案。它使用子字符串和字符串操作函数，而不是像方法1中使用字符串流和向量。

This approach involves manually dividing the input string into substrings, which represent individual words. The substrings are concatenated in reverse order to form the final output string.

算法

• 开始

• 获取输入字符串。

• 初始化两个 size_t 变量 start 和 end，用于保存输入字符串中单词的起始和结束位置。

• 将起始位置初始化为0。

• 找到输入字符串中第一个空格的位置，并将其存储在end变量中。

• 初始化一个空的输出字符串。

• Iterate through the input string and extract words using substrings.

• 从起始位置提取子字符串到结束位置。

• Concatenate the extracted substring in front of the output string, followed by a space.

• Update the start position to the position after the end position.

• Find the next space in the input string starting from the new start position and update the end position.

• 循环结束后，使用

• End

Example

The code is a solution for reversing the order of words in a given string. It does this by dividing the input string into substrings using the find function and concatenating these substrings in reverse order to form the output string. The last space character is then removed from the output string using the pop_back function. This approach is more manual and low-level compared to Approach 1 and requires a deeper understanding of string manipulation. The code takes a given input string, divides it into substrings, reverses the order of these substrings, and returns the final output string.

#include <iostream>
#include <string>

std::string reverseStringByWords(const std::string& input) {
   size_t start = 0;
   size_t end = input.find(' ');
   std::string output;

   while (end != std::string::npos) {
      output = input.substr(start, end - start) + " " + output;
      start = end + 1;
      end = input.find(' ', start);
   }
    
   output = input.substr(start) + " " + output;
   output.pop_back(); // Remove the last space
   return output;
}

int main() {
   std::string input = "Hello, how are you?";
   std::string output = reverseStringByWords(input);
   std::cout << "Input: " << input << std::endl;
   std::cout << "Output: " << output << std::endl;

   return 0;
}

Output

的中文翻译为：

输出

Input: Hello, how are you?
Output: you? are how Hello,

结论

在编程中字符串操作的重要性：掌握字符串操作技术对于任何程序员来说都是至关重要的，因为文本数据在软件开发中无处不在。理解各种字符串操作的方法可以帮助开发人员编写更高效、可维护和健壮的代码。

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