Maximal Rectangle

dynamic  programming

public class Solution {
    public int maximalRectangle(char[][] matrix) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(matrix == null||matrix.length == 0)
            return 0;
        int result = 0;
        int[][] hist = new int[matrix.length][matrix[0].length];
        
        for(int i = 0; i < matrix.length; i++)
            for(int j = 0; j < matrix[0].length; j++){
                if(matrix[i][j] == '1'){
                    if(j == 0)
                        hist[i][j] = 1;
                    else
                        hist[i][j] = hist[i][j-1] + 1;
                }
            }
        
        for(int i = 0; i < matrix.length; i++){
            for(int j = 0; j < matrix[0].length; j++){
                if(hist[i][j] > 0){
                    int column = hist[i][j];
                    int row = 1;
                    while((i+row-1) < matrix.length){
                        if(hist[i+row-1][j] == 0)
                            break;
                        column = Math.min(column, hist[i+row-1][j]);
                        result = Math.max(result, column*row);
                        row++;
                    }
                }
            }
        }
        return result;
    }
}