board.gno

 1package connect4
 2
 3const (
 4	cols = 7
 5	rows = 6
 6)
 7
 8// board is indexed [column][row]; row 0 is the bottom. 0 = empty, 1/2 = player.
 9type board [cols][rows]byte
10
11// drop places piece p in column c (0-based) and returns its row, or -1 if the column is full.
12func (b *board) drop(c int, p byte) int {
13	for r := 0; r < rows; r++ {
14		if b[c][r] == 0 {
15			b[c][r] = p
16			return r
17		}
18	}
19	return -1
20}
21
22// wins reports whether the piece at (c, r) is part of four in a row.
23func (b *board) wins(c, r int) bool { return b.winLine(c, r) != nil }
24
25// winLine returns the cells of the four-or-more line through (c, r), in order
26// along the line, or nil if the piece there completes none.
27func (b *board) winLine(c, r int) [][2]int {
28	p := b[c][r]
29	for _, d := range [4][2]int{{1, 0}, {0, 1}, {1, 1}, {1, -1}} {
30		back := b.count(c, r, -d[0], -d[1], p)
31		n := 1 + back + b.count(c, r, d[0], d[1], p)
32		if n >= 4 {
33			line := make([][2]int, n)
34			for i := range line {
35				k := i - back
36				line[i] = [2]int{c + k*d[0], r + k*d[1]}
37			}
38			return line
39		}
40	}
41	return nil
42}
43
44// count returns how many consecutive p pieces follow (c, r) in direction (dc, dr).
45func (b *board) count(c, r, dc, dr int, p byte) int {
46	n := 0
47	for {
48		c, r = c+dc, r+dr
49		if c < 0 || c >= cols || r < 0 || r >= rows || b[c][r] != p {
50			return n
51		}
52		n++
53	}
54}