Given a matrix mat of size N x M where every element is either O or X.
Replace all O with X that are surrounded by X.
A O (or a set of O) is considered to be surrounded by X if there are X at locations just below, just above, just left and just right of it.
Example 1:
Input: n = 5, m = 4
mat = {{'X', 'X', 'X', 'X'},
{'X', 'O', 'X', 'X'},
{'X', 'O', 'O', 'X'},
{'X', 'O', 'X', 'X'},
{'X', 'X', 'O', 'O'}}
Output: ans = {{'X', 'X', 'X', 'X'},
{'X', 'X', 'X', 'X'},
{'X', 'X', 'X', 'X'},
{'X', 'X', 'X', 'X'},
{'X', 'X', 'O', 'O'}}
Explanation: Following the rule the above
matrix is the resultant matrix.
Your Task:
You do not need to read input or print anything. Your task is to complete the function fill() which takes n, m and mat as input parameters ad returns a 2D array representing the resultant matrix.
Expected Time Complexity: O(nm)
Expected Auxiliary Space: O(nm)
Constraints:
1 ≤ n, m ≤ 500

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