85. Maximal Rectangle

class Solution {
    public int maximalRectangle(char[][] matrix) {
        if(matrix.length==0||matrix[0].length==0)
            return 0;
        int[] heights=new int[matrix[0].length];
        int maxArea=0;
        Stack<Integer> stack=new Stack<Integer>();
        for(int i=0;i<matrix.length;i++)
        {
            for(int j=0;j<matrix[0].length;j++)
                heights[j]=matrix[i][j]=='0'?0:heights[j]+1;
            
            stack.clear();
            for(int j=0;j<=matrix[0].length;j++)
            {
                int h=j==matrix[0].length?0:heights[j];
                if(stack.isEmpty()||heights[stack.peek()]<=h)
                    stack.push(j);
                else
                {
                    int idx=stack.pop();
                    int width=stack.isEmpty()?j:j-stack.peek()-1;
                    maxArea=Math.max(maxArea, heights[idx]*width);
                    j--;
                }
            }
        }
        return maxArea;
    }
}