Problem

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:

11000110000001100011Given the above grid map, return 1.Example 2:11011100000000111011Given the above grid map, return 3.

Notice that:

111and 111are 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.

Solution

class Solution {    public int numDistinctIslands(int[][] grid) {        if (grid == null || grid.length == 0) return 0;        Set
    
      set = new HashSet<>();        for (int i = 0; i < grid.length; i++) {            for (int j = 0; j < grid[0].length; j++) {                if (grid[i][j] == 1) {                    StringBuilder sb = new StringBuilder();                    dfs(grid, i, j, sb, "start:");                    grid[i][j] = 0;                    System.out.println(sb.toString());                    set.add(sb.toString());                }            }        }        return set.size();    }        private void dfs(int[][] grid, int i, int j, StringBuilder sb, String dir) {        if (i < 0 || i == grid.length || j < 0 || j == grid[0].length || grid[i][j] == 0) return;        sb.append(dir);        grid[i][j] = 0;        dfs(grid, i-1, j, sb, "d");        dfs(grid, i+1, j, sb, "u");        dfs(grid, i, j-1, sb, "l");        dfs(grid, i, j+1, sb, "r");        sb.append("#");    }}