c++ - BFS Surrounding -


given nxn grid of 0s, 1s, , 2s, find out whether 1s or 2s surrounded. being surrounded means 1s surrounded 2s or 2s surrounded 1s.

010 121 010

means 2 surround one. there complicated like:

10110 21212 11111

the 2 surround 1 because (2,1) surround 1 , (0,1) not surround 1 because no 1 in left of (0,1).

how determine contains , how solve problem.

assume table a size m*n. should add boundary around table (like following picture) enter image description here

you can that:

  • assume check position (i,j) of table surrounded or not?
  • bfs (i,j) condition (a[u][v] == a[i][j] || a[u][v] == 0) -> add (u,v) stack
  • if visit boundary (a[0][x], a[x][0], a[m+1][x], a[x][n+1]) -> not surrounded

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