Dot Star Regular Expression Matching in C#

using System;
// Dot Star Regular Expression Matching in C#
//
// PURPOSE
// This small matcher supports whole-sequence matching with a wildcard token and repetition
// of the preceding token.
//
// METHOD
// Use a table of prefix matches. A star can omit its preceding token or consume another
// matching text token. A non-star token extends the previous diagonal.
//
// COMPLEXITY
// O(nm) time and O(nm) space. Only dot and star semantics are supported; this is not a full
// regex engine.
//
// CONTRACT
// Tokens >=0 are literal; -1 is dot and -2 is star in the pattern. Star must follow a
// literal or dot, never another star. Returns 1 or 0.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// C# / .NET 10: ReadOnlySpan<int> inputs, Span<int> outputs, primitive workspace arrays,
// Array.BinarySearch for LIS, and checked integer arithmetic. Invalid arguments and overflow
// throw exceptions.
//
// EXAMPLE
// Expected return: 1.
// Run: Use Program.cs in a net10.0 console project; dotnet run.
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

class Program {
    static void alg_require(bool valid) { if (!valid) throw new ArgumentException("invalid algorithm input"); }
    static int alg_size(int n) { alg_require(n>=0 && n<=4000000); return n; }

    static int regex_match(ReadOnlySpan<int> text, ReadOnlySpan<int> pattern) {
        checked {
            int n = text.Length;
            int m = pattern.Length;
            alg_require(((n >= 0) && (n <= 1000000)));
            alg_require(((m >= 0) && (m <= 1000000)));
            alg_require((pattern.Length == m));
            alg_require((text.Length == n));
            for (int alg_i = 0; alg_i < m; alg_i++) {
                alg_require((pattern[alg_i] >= (-2)));
                alg_require(((pattern[alg_i] != (-2)) || ((alg_i > 0) && (pattern[(alg_i - 1)] != (-2)))));
            }
            int[] dp = new int[alg_size(((n + 1) * (m + 1)))];
            dp[0] = 1;
            int i = 0;
            int j = 2;
            while ((j <= m)) {
                if ((pattern[(j - 1)] == (-2))) {
                    dp[j] = dp[(j - 2)];
                }
                j = (j + 1);
            }
            i = 1;
            while ((i <= n)) {
                j = 1;
                while ((j <= m)) {
                    if ((pattern[(j - 1)] == (-2))) {
                        dp[((i * (m + 1)) + j)] = dp[(((i * (m + 1)) + j) - 2)];
                        if (((pattern[(j - 2)] == (-1)) || (pattern[(j - 2)] == text[(i - 1)]))) {
                            dp[((i * (m + 1)) + j)] = Math.Max(dp[((i * (m + 1)) + j)], dp[(((i - 1) * (m + 1)) + j)]);
                        }
                    } else {
                        if (((pattern[(j - 1)] == (-1)) || (pattern[(j - 1)] == text[(i - 1)]))) {
                            dp[((i * (m + 1)) + j)] = dp[((((i - 1) * (m + 1)) + j) - 1)];
                        }
                    }
                    j = (j + 1);
                }
                i = (i + 1);
            }
            return dp[((n * (m + 1)) + m)];
        }
    }

    static void Main() {
        int[] text = new int[] {1, 1, 2};
        int[] pattern = new int[] {1, -2, 2};
        int result = regex_match(text, pattern);
        Console.WriteLine(result);
    }
}