Number of Distinct Islands

Similar Problems:

Given a non-empty 2D array grid of 0’s and 1’s, an island is a group of 1’s (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.

Count the number of distinct islands. An island is considered to be the same as another if and only if one island can be translated (and not rotated or reflected) to equal the other.

Example 1:

11000 11000 00011 00011 Given the above grid map, return 1.

Example 2:

11011 10000 00001 11011 Given the above grid map, return 3.

Notice that:

11 1

and

1 11

are considered different island shapes, because we do not consider reflection / rotation.

Note: The length of each dimension in the given grid does not exceed 50.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

// Blog link: https://code.dennyzhang.com/number-of-distinct-islands // Basic Ideas: dfs + hashmap // Note: In golang, we can't use tuple or slices as key for hashmap // Complexity: Time O(n*m), Space O(n*m*k) // k=num_of_distinct_island import "strconv" var start_x, start_y int func dfs(grid [][]int, i int, j int, island string) string { if i<0 || i>=len(grid) || j<0 || j>=len(grid[0]) { return island } if grid[i][j] != 1 { return island } island += strconv.Itoa((i-start_x)*len(grid) + j-start_y) grid[i][j] = 2 island = dfs(grid, i+1, j, island) island = dfs(grid, i-1, j, island) island = dfs(grid, i, j+1, island) island = dfs(grid, i, j-1, island) return island } func numDistinctIslands(grid [][]int) int { row_count := len(grid) if row_count == 0 { return 0 } hashmap := map[string]bool{} for i, row := range grid { for j, _:= range row { start_x, start_y = i, j if row[j] == 1 { island := dfs(grid, i, j, "") hashmap[island] = true } } } return len(hashmap) }