public int maximalSquare(char[][] matrix) {

int maxSide = 0;

if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {

return maxSide;

}

int rows = matrix.length, columns = matrix[0].length;

int[][] dp = new int[rows][columns];

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

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

if (matrix[i][j] == '1') {

if (i == 0 || j == 0) {

dp[i][j] = 1;

} else {

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

}

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

}

}

}

int maxSquare = maxSide * maxSide;

return maxSquare;

}