BaekJoon1915.java

import java.io.*;
import java.util.StringTokenizer;

public class test {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st = new StringTokenizer(br.readLine());

        int n = Integer.parseInt(st.nextToken());
        int m = Integer.parseInt(st.nextToken());
        int[][] arr = new int[n][m];
        int[][] dp = new int[n][m];

        // 초기화
        int max = 0;
        for (int i=0; i < n; i++) {
            String[] s = br.readLine().split("");
            for (int j = 0; j < m; j++) {
                arr[i][j] = Integer.parseInt(s[j]);
                if (arr[i][j] == 1) {
                    dp[i][j] = 1;
                    max = 1;
                }
            }
        }

        for (int i = 1; i < n; i++) {
            for (int j = 1; j < m; j++) {
                if (arr[i][j] == 1 && arr[i - 1][j - 1] == 1 && arr[i - 1][j] == 1 && arr[i][j - 1] == 1) {
                    dp[i][j] = Math.min(Math.min(dp[i - 1][j], dp[i][j - 1]), dp[i - 1][j - 1]) + 1;
                    max = Math.max(max, dp[i][j]);
                }
            }
        }

        bw.write(String.valueOf(max * max));
        bw.flush();
        bw.close();
        br.close();
    }
}