bitset.all()

Pangram
Pangram in C++

pangram.h

#if !defined(PANGRAM_H)
#define PANGRAM_H
#include <string_view>

namespace pangram {
    bool is_pangram(std::string_view phrase);
}  // namespace pangram

#endif // PANGRAM_H

pangram.cpp

#include "pangram.h"
#include <bitset>
#include <cctype>

namespace pangram {

    bool is_pangram(std::string_view phrase) {
        std::bitset<26> letters;
        for (const auto c : phrase)
            if (std::isalpha(c))
                letters.set (std::tolower(c) - 'a');
        return letters.all();
    }
}  // namespace pangram

This approach starts be defining a bitset to keep track of the used letters.

A range-based for loop iterates over all of the characters in the input phrase string_view. Each character is tested by the isalpha() function to see if it is considered an alphabetic character according to the currently installed C locale. If the currently installed locale is not suitable for the English alphabet, then std::locale::classic() can be passed to the isalpha() function defined in <locale>, like so:

#include <bitset>
#include <locale>

// code snipped

if (std::isalpha(c, std::locale::classic()))

If the character is alphabetic, then a bit value is set to represent its being used. The ASCII value of a is subtracted from the character tolower()ed. If the currently installed locale is not suitable for lowercasing English characters, then std::locale::classic() can be passed to the tolower() function defined in <locale>, like so:

#include <bitset>
#include <locale>

// code snipped

letters.set (std::tolower(c, std::locale::classic()) - 'a');

For example, if the character is A, then A is lowered to a, and the ASCII value of a is subtracted by the ASCII value a to set the bit at position 0 in the bitset to 1.

if the character is Z, then Z is lowered to z, and the ASCII value of z is subtracted by the ASCII value a to set the bit at position 25 in the bitset to 1.

After all of the characters in the input phrase are iterated, the the all() function is used to return if all of the 26 bits are set.

22nd May 2024 · Found it useful?