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Zig arrays to be stack-allocated #354

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Zig arrays to be stack-allocated #354

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5f427f3
Zig arrays to be stack-allocated
PDeveloper Jan 13, 2025
853ba69
Zig levenshtein remove equality check
PDeveloper Jan 13, 2025
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28 changes: 10 additions & 18 deletions levenshtein/zig/code.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -3,9 +3,8 @@ const std = @import("std");
/// Calculates the Levenshtein distance between two strings using Wagner-Fischer algorithm
/// Space Complexity: O(min(m,n)) - only uses two arrays instead of full matrix
/// Time Complexity: O(m*n) where m and n are the lengths of the input strings
fn levenshteinDistance(s1: []const u8, s2: []const u8, prev_row: []usize, curr_row: []usize) usize {
fn levenshteinDistance(s1: []const u8, s2: []const u8) usize {
// Early termination checks
if (std.mem.eql(u8, s1, s2)) return 0;
if (s1.len == 0) return s2.len;
if (s2.len == 0) return s1.len;

Expand All @@ -16,6 +15,10 @@ fn levenshteinDistance(s1: []const u8, s2: []const u8, prev_row: []usize, curr_r
const m = str1.len;
const n = str2.len;

// Initialize arrays
var prev_row: [1024]usize = undefined;
var curr_row: [1024]usize = undefined;
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this is broken code and will panic with some inputs. C is doing VLAs which is also broken (e.g,. very large strings that overflow the stack).


// Initialize first row
for (0..m + 1) |i| {
prev_row[i] = i;
Expand All @@ -30,8 +33,7 @@ fn levenshteinDistance(s1: []const u8, s2: []const u8, prev_row: []usize, curr_r
const cost: usize = if (str1[i - 1] == str2[j - 1]) 0 else 1;

// Calculate minimum of three operations
curr_row[i] = @min(
prev_row[i] + 1, // deletion
curr_row[i] = @min(prev_row[i] + 1, // deletion
curr_row[i - 1] + 1, // insertion
prev_row[i - 1] + cost // substitution
);
Expand All @@ -57,27 +59,17 @@ pub fn main() !void {
std.process.exit(1);
}

// Calculate length of longest input string
const input_lengths = try allocator.alloc(usize, args.len);
for (0..input_lengths.len) |i| input_lengths[i] = args[i].len;

const max_inp_len = std.mem.max(usize, input_lengths);

// Reuse prev and curr row to minimize allocations
const prev_row = try allocator.alloc(usize, max_inp_len);
const curr_row = try allocator.alloc(usize, max_inp_len);

var min_distance: isize = -1;
var min_distance: usize = std.math.maxInt(usize);
var times: usize = 0;

// Compare all pairs of strings

for (1..args.len) |i| {
for (1..args.len) |j| {
if (i != j) {
const distance = levenshteinDistance(args[i], args[j], prev_row, curr_row);
if (min_distance == -1 or distance < @as(usize, @intCast(min_distance))) {
min_distance = @as(isize, @intCast(distance));
const distance = levenshteinDistance(args[i], args[j]);
if (distance < min_distance) {
min_distance = distance;
}
times += 1;
}
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