Count neighbouring live cells
In a grid-based game, count how many of the eight surrounding cells around a given position hold a value of 1.
- Check all eight directions: orthogonal and diagonal.
- Cells outside the grid boundary are ignored.
- The cell at the given position itself is never counted.
boardNeighbours(grid: list<list<int>>, row: int, col: int) → int
Go needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
func boardNeighbours(grid [][]int, row int, col int) int {
}Worked examples
| Call | Result |
|---|---|
boardNeighbours([][]int{[]int{1, 1, 1}, []int{1, 0, 1}, []int{1, 1, 1}}, 1, 1) | 8 |
boardNeighbours([][]int{[]int{0, 0, 0}, []int{0, 1, 0}, []int{0, 0, 0}}, 1, 1) | 0 |
boardNeighbours([][]int{[]int{1, 1}, []int{1, 1}}, 0, 0) | 3 |
boardNeighbours([][]int{[]int{1, 0, 1}, []int{0, 1, 0}, []int{1, 0, 1}}, 1, 1) | 4 |
Hint
Loop over offsets from -1 to +1 in both axes, skip (0,0), and bounds-check each neighbour.
Reference solution in Go
func boardNeighbours(grid [][]int, row int, col int) int {
count := 0
rows := len(grid)
cols := len(grid[0])
for dr := -1; dr <= 1; dr++ {
for dc := -1; dc <= 1; dc++ {
if dr == 0 && dc == 0 {
continue
}
r, c := row+dr, col+dc
if r >= 0 && r < rows && c >= 0 && c < cols && grid[r][c] == 1 {
count++
}
}
}
return count
}