public int solution(int [][]board) {

int N = board.length;

int M = board[0].length;

int[][] dp = new int[N][M];

// dp배열 초기화

int len = 0;

for (int i = 0; i < N; i++) {

for (int j = 0; j < M; j++) {

dp[i][j] = board[i][j];

if (dp[i][j]==1) len = 1;

}

}

for (int i = 1; i < N; i++) {

for (int j = 1; j < M; j++) {

if (board[i][j]==0) continue;

dp[i][j] = Math.min(Math.min(dp[i - 1][j], dp[i][j - 1]), dp[i - 1][j - 1]) + 1;

len = Math.max(len, dp[i][j]);

}

}

return len*len;

}