diff options
| -rw-r--r-- | build.zig | 4 | ||||
| -rw-r--r-- | exercises/098_bit_manipulation2.zig | 63 | ||||
| -rw-r--r-- | patches/patches/098_bit_manipulation2.patch | 4 |
3 files changed, 71 insertions, 0 deletions
@@ -509,6 +509,10 @@ const exercises = [_]Exercise{ .output = "x = 0; y = 1", }, .{ + .main_file = "098_bit_manipulation2.zig", + .output = "Is this a pangram? true!", + }, + .{ .main_file = "999_the_end.zig", .output = "\nThis is the end for now!\nWe hope you had fun and were able to learn a lot, so visit us again when the next exercises are available.", }, diff --git a/exercises/098_bit_manipulation2.zig b/exercises/098_bit_manipulation2.zig new file mode 100644 index 0000000..34b7136 --- /dev/null +++ b/exercises/098_bit_manipulation2.zig @@ -0,0 +1,63 @@ +// Another useful practice for bit manipulation is setting bits as flags. +// This is especially useful when processing lists of something and storing +// the states of the entries, e.g. a list of numbers and for each prime +// number a flag is set. +// +// As an example, let's take the Pangram exercise from Exercism: +// https://exercism.org/tracks/zig/exercises/pangram +// +// A pangram is a sentence using every letter of the alphabet at least once. +// It is case insensitive, so it doesn't matter if a letter is lower-case +// or upper-case. The best known English pangram is: +// +// "The quick brown fox jumps over the lazy dog." +// +// There are several ways to select the letters that appear in the pangram +// (and it doesn't matter if they appear once or several times). +// +// For example, you could take an array of bool and set the value to 'true' +// for each letter in the order of the alphabet (a=0; b=1; etc.) found in +// the sentence. However, this is neither memory efficient nor particularly +// fast. Instead we take a simpler way, very similar in principle, we define +// a variable with at least 26 bits (e.g. u32) and also set the bit for each +// letter found at the corresponding position. +// +// Zig provides functions for this in the standard library, but we prefer to +// solve it without these extras, after all we want to learn something. +// +const std = @import("std"); +const ascii = std.ascii; +const print = std.debug.print; + +pub fn main() !void { + // let's check the pangram + print("Is this a pangram? {?}!\n", .{isPangram("The quick brown fox jumps over the lazy dog.")}); +} + +fn isPangram(str: []const u8) bool { + // first we check if the string has at least 26 characters + if (str.len < 26) return false; + + // we uses a 32 bit variable of which we need 26 bit + var bits: u32 = 0; + + // loop about all characters in the string + for (str) |c| { + // if the character is an alphabetical character + if (ascii.isASCII(c) and ascii.isAlphabetic(c)) { + // then we set the bit at the position + // + // to do this, we use a little trick: + // since the letters in the ASCI table start at 65 + // and are numbered by, we simply subtract the first + // letter (in this case the 'a') from the character + // found, and thus get the position of the desired bit + bits |= @as(u32, 1) << @truncate(u5, ascii.toLower(c) - 'a'); + } + } + // last we return the comparison if all 26 bits are set, + // and if so, we know the given string is a pangram + // + // but what do we have to compare? + return bits == 0x..???; +} diff --git a/patches/patches/098_bit_manipulation2.patch b/patches/patches/098_bit_manipulation2.patch new file mode 100644 index 0000000..1b5df35 --- /dev/null +++ b/patches/patches/098_bit_manipulation2.patch @@ -0,0 +1,4 @@ +62c62 +< return bits == 0x..???; +--- +> return bits == 0x3ffffff; |