FastPrep
Problem · Matrix

Number of Distinct Islands (For L5 :)

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In an ocean, there are islands marked by 1. Water is represented by 0. Determine how many unique shapes (no rotation or mirror) among these islands. Islands are connected 4-directionally.

Function Description

Complete the function numDistinctIslands in the editor.

numDistinctIslands has the following parameter:

  1. int[][] grid: a 2D array of integers representing the ocean

Returns

int: the number of unique island shapes

Examples
01 · Example 1
grid = [[1, 1, 1, 1, 0, 0], [1, 1, 0, 0, 0, 1], [0, 0, 1, 1, 0, 1], [1, 1, 0, 0, 0, 0], [0, 0, 1, 1, 1, 1], [1, 0, 1, 1, 0, 0]]
return = 4
There are 4 unique island shapes:
  • the 2 6-sized islands,
  • the 2 2-sized islands,
  • the 1 2-sized island,
  • the 1 1-sized island.
Standard BFS/DFS problem with a translation of the starting point to the origin of each island. The solution is done correctly and optimally with O(n) complexity.
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public int numDistinctIslands(int[][] grid) {
  // write your code here
}
grid[[1, 1, 1, 1, 0, 0], [1, 1, 0, 0, 0, 1], [0, 0, 1, 1, 0, 1], [1, 1, 0, 0, 0, 0], [0, 0, 1, 1, 1, 1], [1, 0, 1, 1, 0, 0]]
expected4
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