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Number of Islands

Medium
VerifiedBFSDFSMatrixUnion Find~20 min

You’re given a grid of 0 (water) and 1 (land). An island is a maximal group of land cells connected 4-directionally.

Return the number of islands. The input is the grid number[][] directly.

Examples

in[[1,1,0,0,0],[1,1,0,0,0],[0,0,1,0,0],[0,0,0,1,1]]
out3

Three separate land masses.

in[[1,1,1,1,0],[1,1,0,1,0],[1,1,0,0,0],[0,0,0,0,0]]
out1

All land cells connect into one island.

Constraints

  • 1 ≤ rows, cols ≤ 300
  • grid[r][c] is 0 (water) or 1 (land).
  • Islands connect 4-directionally.

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