通过回测法求出所有满足的区域，
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在回潮的同时记录其入口坐标，入口个数大于1则不符合要求;，
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入口个数等于1时，判断其区域大小;
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如果存在多个区域，且区域大小相同，则只需记录其大小; 其他情况则需要记录区域最大值和横纵坐标
关键代码：
public interface Runnable {
public static void main(String[] args) {
// 处理输入
Scanner in = new Scanner(System.in);
int m = in.nextInt();
int n = in.nextInt();
Character[][] matrix = new Character[m][n];
in.nextLine();
for (int i = 0; i < m; i++) {
String[] strs = in.nextLine().split(" ");
for (int j = 0; j < n; j++) {
matrix[i][j] = strs[j].charAt(0);
}
}
//最大的区域大小
int max_area = 0;
// 记录单入口区域的入口坐标，区域大小
HashMap<String, Integer> zones = new HashMap<>();
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (matrix[i][j] == 'O' && (i == 0 || j == 0 || i == m - 1 || j == n - 1)) {
//先假定当前可以为入口
int area = calc_area(copy(matrix), i, j, true);
if (area > 0) {
String key = i + " " + j;
zones.put(key, area);
if (area > max_area) {
max_area = area;
}
}
}
}
}
//输出
String max_entrace = "";
for (Map.Entry<String, Integer> e : zones.entrySet()) {
if (e.getValue() == max_area) {
if (max_entrace.isEmpty()) {
max_entrace = e.getKey();
} else {
max_entrace = "more";
break;
}
}
}
if (max_area == 0) {
System.out.println("NULL");
} else if (max_entrace == "more") {
System.out.println(max_area);
} else {
System.out.println(max_entrace + " " + max_area);
}
}
public static Character[][] copy(Character[][] a) {
int m = a.length;
int n = a[0].length;
Character[][] matrix = new Character[m][n];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
matrix[i][j] = a[i][j];
}
}
return matrix;
}
// i, j为入口的区域大小，
public static int calc_area(Character[][] matrix, int i, int j, boolean flag) {
if (!flag) {
// 遍历到边界时，说明有其他入口，则不是单入口
if (i == 0 || i == matrix.length - 1 || j == 0 || j == matrix[0].length - 1) {
return 0;
}
}
matrix[i][j] = 'X';
// 记录区域大小
int count = 1;
int[][] directions = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
for (int[] direction : directions) {
int newX = i + direction[0], newY = j + direction[1];
if (newX >= 0 && newX < matrix.length && newY >= 0 && newY < matrix[0].length
&& matrix[newX][newY] == 'O') {
int count1 = calc_area(matrix, newX, newY, false);
if (count1 == 0) {
return 0;
}
count += count1;
}
}
return count;
}