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As_1162.java
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As_1162.java
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import java.util.*;
class As_1162 {
// My first solution: BFS
public int maxDistance(int[][] grid) {
int R = grid.length;
int C = grid[0].length;
boolean[][] visited = new boolean[R][C];
Deque<int[]> q = new ArrayDeque<>();
for (int i = 0; i < R; i++) {
for (int j = 0; j < C; j++) {
if (grid[i][j] == 1) {
visited[i][j] = true;
q.add(new int[]{i, j});
}
}
}
if (q.size() == 0 || q.size() == R * C) {
return -1;
}
int res = 0;
int[][] directions = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
while (!q.isEmpty()) {
int len = q.size();
for (int k = 0; k < len; k++) {
int[] start = q.removeFirst();
for (int[] d : directions) {
int x = start[0] + d[0];
int y = start[1] + d[1];
if (x >= 0 && x < R && y >= 0 && y < C && !visited[x][y]) {
visited[x][y] = true;
q.add(new int[]{x, y});
}
}
}
if (!q.isEmpty()) res++;
}
return res;
}
}