reorg and add code for second edition

11_dynamic_programming/zig/longest_common_subsequence.zig

@@ -0,0 +1,63 @@
+const std = @import("std");
+const heap = std.heap;
+const math = std.math;
+const expect = std.testing.expect;
+
+pub fn main() !void {
+    var gpa = heap.GeneralPurposeAllocator(.{}){};
+    var arena = heap.ArenaAllocator.init(gpa.allocator());
+    defer arena.deinit();
+
+    var n = try subsequence(arena.allocator(), "fish", "fosh");
+    std.debug.print("{d}\n", .{n});
+}
+
+fn subsequence(allocator: std.mem.Allocator, a: []const u8, b: []const u8) !u32 {
+    var grid = try allocator.alloc([]u32, a.len + 1);
+
+    for (grid) |*row| {
+        row.* = try allocator.alloc(u32, b.len + 1);
+        for (row.*) |*cell| {
+            cell.* = 0;
+        }
+    }
+
+    var i: usize = 1;
+    while (i <= a.len) : (i += 1) {
+        var j: usize = 1;
+        while (j <= b.len) : (j += 1) {
+            if (a[i - 1] == b[j - 1]) {
+                grid[i][j] = grid[i - 1][j - 1] + 1;
+            } else {
+                grid[i][j] = math.max(grid[i][j - 1], grid[i - 1][j]);
+            }
+        }
+    }
+
+    return grid[a.len][b.len];
+}
+
+test "subsequence" {
+    var tests = [_]struct {
+        a: []const u8,
+        b: []const u8,
+        exp: u32,
+    }{
+        .{ .a = "abc", .b = "abcd", .exp = 3 },
+        .{ .a = "pera", .b = "mela", .exp = 2 },
+        .{ .a = "banana", .b = "kiwi", .exp = 0 },
+    };
+
+    for (tests) |t| {
+        var gpa = heap.GeneralPurposeAllocator(.{}){};
+        var arena = heap.ArenaAllocator.init(gpa.allocator());
+        defer {
+            arena.deinit();
+            const leaked = gpa.deinit();
+            if (leaked) std.testing.expect(false) catch @panic("TEST FAIL"); //fail test; can't try in defer as defer is executed after we return
+        }
+
+        var n = try subsequence(arena.allocator(), t.a, t.b);
+        try expect(n == t.exp);
+    }
+}