geeksforgeeks: find the number of islands

geeksforgeeks/find-the-number-of-islands/README.md

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+# Find the number of islands
+
+Given a binary 2D matrix, find the number of islands.
+A group of connected 1s (horizontal, vertical, diagonal) forms an island.
+
+## Copyright Notice
+
+This problem is based on [content](https://www.geeksforgeeks.org/find-the-number-of-islands-using-dfs/)
+from [GeeksforGeeks](https://www.geeksforgeeks.org)
+written by GeeksforGeeks
+and subject to [GeeksforGeeks copyright](https://www.geeksforgeeks.org/legal/copyright-information/).
+The original content from GeeksforGeeks and any modifications made here are attributed to GeeksforGeeks contributors,
+and this work is shared under [CC BY-SA 4.0](../LICENSE).

geeksforgeeks/find-the-number-of-islands/solution.go

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+package find_the_number_of_islands
+
+func Solution(matrix [][]int) int {
+	if len(matrix) == 0 || len(matrix[0]) == 0 {
+		return 0
+	}
+
+	rows, cols := len(matrix), len(matrix[0])
+	var islands int
+	for r := 0; r < rows; r++ {
+		for c := 0; c < cols; c++ {
+			if matrix[r][c] == 1 {
+				islands++
+				dfs(matrix, rows, cols, r, c)
+			}
+		}
+	}
+
+	return islands
+}
+
+func dfs(matrix [][]int, rows, cols, r, c int) {
+	if r < 0 || r >= rows ||
+		c < 0 || c >= cols ||
+		matrix[r][c] == 0 {
+		return
+	}
+
+	matrix[r][c] = 0
+	dfs(matrix, rows, cols, r-1, c-1)
+	dfs(matrix, rows, cols, r-1, c)
+	dfs(matrix, rows, cols, r-1, c+1)
+	dfs(matrix, rows, cols, r, c-1)
+	dfs(matrix, rows, cols, r, c+1)
+	dfs(matrix, rows, cols, r+1, c-1)
+	dfs(matrix, rows, cols, r+1, c)
+	dfs(matrix, rows, cols, r+1, c+1)
+}

geeksforgeeks/find-the-number-of-islands/solution_test.go

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+package find_the_number_of_islands_test
+
+import (
+	"testing"
+
+	sut "github.com/minizilla/minmax/geeksforgeeks/find-the-number-of-islands"
+	"github.com/minizilla/testr"
+)
+
+func TestFindTheNumberOfIslands(t *testing.T) {
+	tests := map[string]struct {
+		matrix  [][]int
+		islands int
+	}{
+		"zero": {nil, 0},
+		"one": {
+			[][]int{
+				{0, 1},
+				{1, 0},
+			}, 1,
+		},
+		"two": {
+			[][]int{
+				{0, 1, 0, 0, 0},
+				{1, 0, 0, 1, 1},
+			}, 2,
+		},
+		"three": {
+			[][]int{
+				{1, 0, 1, 1},
+				{0, 1, 0, 1},
+				{0, 0, 0, 0},
+				{0, 1, 0, 0},
+				{0, 0, 1, 0},
+				{1, 0, 0, 0},
+			}, 3,
+		},
+		"four": {
+			[][]int{
+				{1, 0, 1, 0, 1, 0, 0, 1, 0},
+				{0, 1, 0, 1, 0, 0, 1, 0, 1},
+				{0, 0, 0, 0, 0, 0, 0, 1, 0},
+				{1, 1, 0, 0, 0, 1, 0, 1, 0},
+			}, 4,
+		},
+	}
+
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			assert := testr.New(t)
+			islands := sut.Solution(tc.matrix)
+			assert.Equal(islands, tc.islands)
+		})
+	}
+}