GESP Level 3 C++ Practice (Strings) luogu-B2156 Longest Word 2

GESP Level 3 practice, string exercises (Knowledge point 6 in the C++ Level 3 syllabus), difficulty ★★☆☆☆.

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luogu-B2156 Longest Word 2

Problem Requirements

Problem Description

A simple English sentence ending with ., with words separated by spaces, containing no abbreviations or other special forms, find the longest word in the sentence.

Input Format

A simple English sentence ending with . (length not exceeding ), with words separated by spaces, containing no abbreviations or other special forms.

Output Format

The longest word in the sentence. If there are multiple, output the first one.

Input Output Example #1

Input #1

I am a student of Peking University.

Output #1

University

Problem Analysis

Solution Approach

Read a line of English sentence and store it in a string variable
Traverse the sentence to count word lengths:

Define variables to record the current word length and the longest word length
Define a variable to store the longest word

Process words:

When encountering a letter, increment the current word length by 1
When encountering a space, compare the current word length with the longest word length
If the current word is longer, update the longest word and its length
Reset the current word length to 0

Special handling for the last word (excluding the period):

Compare the last word length with the longest word length
If the last word is longer, update the longest word

Output the longest word

Complexity Analysis:

Time complexity is , where n is the length of the sentence
Space complexity is , where m is the length of the longest word

Example Code

#include <iostream>
#include <string>

int main() {
    // Define a string variable to store the input sentence
    std::string str;
    // Read a line of input, including spaces
    getline(std::cin, str);
    // Record the length of the longest word
    int max_count = 0;
    // Record the length of the current word
    int count = 0;
    // Store the longest word
    std::string max_str;
    // Traverse the string, note that subtracting 1 is to avoid processing the last period
    for (int i = 0; i < str.size() - 1; i++) {
        // If not a space, it is part of a word
        if (str[i] != ' ') {
            count++;
        } else {
            // When encountering a space, check if the current word is the longest
            if (count > max_count) {
                // Extract the longest word and save it
                max_str = str.substr(i - count, count);
                max_count = count;
            }
            // Reset the current word length counter
            count = 0;
        }
    }
    // Handle the last word (excluding the period)
    if (count > max_count) {
        max_str = str.substr(str.size() - 1 - count, count);
    }
    // Output the longest word
    std::cout << max_str << std::endl;
    return 0;
}

Additionally, using cin for direct input makes the code more concise

#include <iostream>
#include <string>

int main() {
    std::string str;           // Variable to store each word read
    int max_count = 0;         // Record the length of the longest word
    std::string max_str;       // Store the longest word

    // Loop to read words until EOF or input ends
    while(std::cin >> str) {
        // If the word ends with a period, remove the period
        if (str.back() == '.') {
            str.pop_back();
        }
        
        int str_length = str.length();  // Get the length of the current word
        
        // If the current word length is greater than the recorded longest length
        if (str_length > max_count) {
            max_count = str_length;     // Update the longest length
            max_str = str;              // Update the longest word
        }
    }
    
    // Output the longest word
    std::cout << max_str << std::endl;
    return 0;
}

When debugging the above code locally, you may need to exit the loop using Ctrl+Z. However, on platforms like Luogu, you can test it through the provided tests. You can also automatically exit the loop by checking if the string ends with . and using break to exit the loop.

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

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