public class MaximalSquare {

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

if (matrix == null || matrix.length < 1 || matrix[0].length < 1) {

return 0;

}

int height = matrix.length;

int width = matrix[0].length;

int maxSide = 0;

// 相当于已经预处理新增第一行、第一列均为0

int[][] dp = new int[height + 1][width + 1];

for (int row = 0; row < height; row++) {

for (int col = 0; col < width; col++) {

if (chekIsOne(matrix[row][col])) {

dp[row + 1][col + 1] = Math.min(Math.min(dp[row + 1][col], dp[row][col + 1]), dp[row][col]) + 1;

maxSide = Math.max(maxSide, dp[row + 1][col + 1]);

}

}

}

return maxSide * maxSide;

}

private boolean chekIsOne(char ch) {

return Character.getNumericValue(ch) == 1;

}

}