GESP Level 3 C++ Practice (Strings) luogu-B2122 Word Reversal

GESP Level 3 Practice, String Exercise (Knowledge Point 6 in the C++ Level 3 Syllabus), Difficulty ★★☆☆☆.

• GESP Level 1 Practice Question List

• GESP Level 1 Real Question List

• GESP Level 2 Practice Question List

• GESP Level 2 Real Question List

• GESP Level 3 Practice Question List

• GESP Level 3 Real Question List

• GESP Level 4 Practice Question List

• GESP Level 4 Real Question List

• GESP Level 1-5 Syllabus Analysis

luogu-B2122 Word Reversal

Problem Requirements

Problem Description

When writing words, Xiaoming likes to write them backwards. For example, <span>hello</span> he writes as <span>olleh</span>. Given a sentence written by Xiaoming, please restore all the words.

Input Format

One line, a string representing the sentence, with words separated by spaces.

Output Format

Each word on a new line.

Input Output Example #1

Input #1

olleh dlrow

Output #1

hello
world

Notes/Tips

The length of the sentence does not exceed , only contains lowercase letters and spaces, and there are no extra spaces.

Problem Analysis

Solution Approach

1. Read a complete line of input sentence, which contains only lowercase letters and spaces.
2. Iterate through each character in the sentence:

• Reverse the current word (reverse the order of letters).
• Output the reversed word.
• Clear the current word to prepare for the next word.

• When encountering a letter, add it to the current word.
• When encountering a space:

After the iteration ends, process the last word:

• Reverse the last word.
• Output the reversed word.

Complexity Analysis:

• The time complexity is , where n is the total length of the input sentence.
• The space complexity is , where w is the maximum length of a single word.

Example Code

Method 1: Using stringstream and reverse function

#include <algorithm>
#include <iostream>
#include <sstream>

int main() {
    // Define a string variable to store the input sentence
    std::string str;
    // Read a complete line of input
    std::getline(std::cin, str);
    // Create a string stream to split words
    std::stringstream ss(str);
    // Define a string variable to store each word
    std::string token;
    // Use getline to split the string stream by spaces
    while (std::getline(ss, token, ' ')) {
        // Reverse each word
        reverse(token.begin(), token.end());
        // Output the reversed word
        std::cout << token << std::endl;
    }
    return 0;
}

Method 2: Manually processing the string

#include <string>
#include <iostream>

int main() {
    // Define a string variable to store the input sentence
    std::string str;
    // Read a complete line of input
    std::getline(std::cin, str);
    // Define a string variable to store the current word being processed
    std::string cur_str;
    // Iterate through the input string
    for (int i = 0; i < str.length(); i++) {
        // If a space is encountered, the current word is complete
        if (str[i] == ' ') {
            // Output the currently reversed word
            std::cout << cur_str << std::endl;
            // Clear the current word to prepare for the next
            cur_str = "";
        } else {
            // Add the current character to the front of the word to achieve reversal
            cur_str = str[i] + cur_str;
        }
    }
    // Output the last word (since there is no space after the last word)
    std::cout << cur_str << std::endl;
    return 0;
}

For detailed GESP syllabus, real questions explanations, knowledge expansion, and practice lists, see:

[Top][GESP] C++ Certification Learning Resource Summary

“luogu-” series questions can be evaluated online at Luogu Question Bank.

“bcqm-” series questions can be evaluated online at Programming Enlightenment Question Bank.