最大正方形

// 最大正方形  
// 在一个由 '0' 和 '1' 组成的二维矩阵内，找到只包含 '1' 的最大正方形，并返回其面积。  
// 输入：matrix = [["1","0","1","0","0"],["1","0","1","1","1"],["1","1","1","1","1"],["1","0","0","1","0"]]  
// 输出：4  
public static 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;  
}