gistfile1.txt

Given a matrix consists of 0 and 1, find the distance of the nearest 0 for each cell.

The distance between two adjacent cells is 1.
Example 1: 
Input:

0 0 0
0 1 0
0 0 0
Output:
0 0 0
0 1 0
0 0 0
Example 2: 
Input:

0 0 0
0 1 0
1 1 1




-1 -1 -1
-1 0 -1
 -1 -1

Output:
0 0 0
0 1 0
1 2 1

keywords:

matrix, value only 0 and 1, 
statement: the distance two adjacent cell is 1
left, right, up or down , at most 4 adajcent cells 


ask: find distance of nearest 0 for each cell

if cell value is 0, no change
if cell value is 1, 

0 0 0
0 1 0
0 0 0

0 0 0
0 1 0
1 2 1  <--