2257. Count Unguarded Cells in the Grid
Medium
You are given two integers
m
and n
representing a 0-indexed m x n
grid. You are also given two 2D integer arrays guards
and walls
where guards[i] = [rowi, coli]
and walls[j] = [rowj, colj]
represent the positions of the ith
guard and jth
wall respectively.A guard can see every cell in the four cardinal directions (north, east, south, or west) starting from their position unless obstructed by a wall or another guard. A cell is guarded if there is at least one guard that can see it.
Return the number of unoccupied cells that are not guarded.
Example 1:

Input: m = 4, n = 6, guards = [[0,0],[1,1],[2,3]], walls = [[0,1],[2,2],[1,4]]
Output:
7
Explanation:
The guarded and unguarded cells are shown in red and green respectively in the above diagram.
There are a total of 7 unguarded cells, so we return 7.
Example 2:

Input: m = 3, n = 3, guards = [[1,1]], walls = [[0,1],[1,0],[2,1],[1,2]]
Output:
4
Explanation:
The unguarded cells are shown in green in the above diagram.
There are a total of 4 unguarded cells, so we return 4.
Constraints:
1 <= m, n <= 105
2 <= m * n <= 105
1 <= guards.length, walls.length <= 5 * 104
2 <= guards.length + walls.length <= m * n
guards[i].length == walls[j].length == 2
0 <= rowi, rowj < m
0 <= coli, colj < n
- All the positions in
guards
andwalls
are unique.
func countUnguarded(m int, n int, guards [][]int, walls [][]int) int {
land := make([][]byte, m)
for i := range land {
land[i] = make([]byte, n)
}
for _, wall := range walls {
land[wall[0]][wall[1]] = 'W'
}
for _, guard := range guards {
x := guard[0]
y := guard[1]
land[x][y] = 'G'
for i:=x+1; i<m; i++ {
if (land[i][y]=='W') || (land[i][y]=='G') { break }
land[i][y] = 'A'
}
for i:=x-1; i>=0; i-- {
if (land[i][y]=='W') || (land[i][y]=='G') { break }
land[i][y] = 'A'
}
for j:=y+1; j<n; j++ {
if (land[x][j]=='W') || (land[x][j]=='G') { break }
land[x][j] = 'A'
}
for j:=y-1; j>=0; j-- {
if (land[x][j]=='W') || (land[x][j]=='G') { break }
land[x][j] = 'A'
}
}
ans := 0
for i:=0; i<m; i++ {
for j:=0; j<n; j++ {
if land[i][j]!='W' && land[i][j]!='G' && land[i][j]!='A' {
ans++
}
}
}
return ans
}