Sphere Online Judge

SPOJ Problem Set (classical)

206. Bitmap

Problem code: BITMAP

There is given a rectangular bitmap of size n*m. Each pixel of the bitmap is either white or black, but at least one is white. The pixel in i-th line and j-th column is called the pixel (i,j). The distance between two pixels p1=(i1,j1) and p2=(i2,j2) is defined as:



Write a program which:

  • reads the description of the bitmap from the standard input,
  • for each pixel, computes the distance to the nearest white pixel,
  • writes the results to the standard output.


The number of test cases t is in the first line of input, then t test cases follow separated by an empty line. In the first line of each test case there is a pair of integer numbers n, m separated by a single space, 1<=n <=182, 1<=m<=182. In each of the following n lines of the test case exactly one zero-one word of length m, the description of one line of the bitmap, is written. On the j-th position in the line (i+1), 1 <= i <= n, 1 <= j <= m, is '1' if, and only if the pixel (i,j) is white.


In the i-th line for each test case, 1<=i<=n, there should be written m integers f(i,1),...,f(i,m) separated by single spaces, where f(i,j) is the distance from the pixel (i,j) to the nearest white pixel.


Sample input:
3 4

Sample output:
3 2 1 0
2 1 0 0
1 0 0 1

Added by:Piotr Łowiec
Time limit:4s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel Pentium G860 3GHz)
Resource:6th Polish Olympiad in Informatics, stage 2

hide comments
2014-12-12 12:47:48 piyush
nice problem
after so many TLE and Runtime
finally AC :)
2014-12-12 11:42:38 Swapnil Borse
A simple approach can be make a note of all the indices (x,y) where one appears and then spread out in all the directions if you are taking a 2D array. No question of TLE then. Mine got accepted in first attempt with 0.07s :P
2014-12-12 05:47:22 `AkaY
taking int 2D array costed me two wa :( taking the char 2D array same code got AC :)
2014-12-05 07:12:47 Sudharsansai
Nice question!Learnt a new thing.
2014-10-31 21:20:51 1yr
no need of bfs or dfs
2014-10-31 21:20:46 1yr

Last edit: 2014-10-31 21:21:29
2014-10-11 15:02:42 അഭി
single BFS from multiple source nodes
2014-10-10 12:21:53 Master_Card
Very good question!!
2014-09-27 09:21:20 mayank
dfs requires a lot of optimisation. Vector->Array, and currentDepth->Distance. :P
2014-09-27 08:01:10 sg
awesome problem!!
learnt a lot..
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