static public int maximalRectangle(char[][] matrix) {

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

			return 0;

		int result=0;

		int[] dp=new int[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')

					dp[j]++;

				else dp[j]=0;

			result=Math.max(result, largestRectangleArea(dp));

		}

		return result;

	}

	 public static int largestRectangleArea(int[] height) {

	        Stack<Integer> stk = new Stack<Integer>();

	        int ret = 0;

	        for (int i = 0; i <= height.length; i++) {

	            int h=0;

	            if(i<height.length)

	                h=height[i];

	            if (stk.isEmpty() || h >= height[stk.peek()])

	                stk.push(i);

	            else {

	                int top = stk.pop();

	                ret = Math.max(ret, height[top] * (stk.empty() ? i : i - stk.peek() - 1));

	                i--;

	            }

	        }

	        return ret;

	}