85. 最大矩形

85. 最大矩形

class Solution {
   
    public int maximalRectangle(char[][] matrix) {
   
        int m = matrix.length, n = matrix[0].length;
        int[] heights = new int[n];
        int res = 0;

        for(int i = 0; i < m; i++){
   
            for(int j = 0; j < n; j++){
   
                if(matrix[i][j] == '1') heights[j]++;
                else heights[j] = 0;
            }
            res = Math.max(res, largestRectangleArea(heights));
        }

        return res;
    }

    int largestRectangleArea(int[] heights) {
   
        int len = heights.length + 2;
        int[] newHeight = new int[len];
        for(int i = 1; i < len - 1; i++) newHeight[i] = heights[i - 1];

        Deque<Integer> stack = new ArrayDeque<>();
        int res = 0;

        for(int i = 0; i < len; i++){
   
            while(!stack.isEmpty() && newHeight[i] < newHeight[stack.peek()]){
   
                int pop = stack.pop();
                int w = i - stack.peek() - 1;
                int h = newHeight[pop];
                int area = h * w;
                res = Math.max(res, area);
            }
            stack.push(i);
        }

        return res;
    }
}