Maximal Rectangle

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing all ones and return its area.

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方法是 largest rectangle in histogram + dp

public class Solution {
    public int maximalRectangle(char[][] matrix) {
        if (matrix.length == 0 || matrix[0].length == 0) {
            return 0;
        }
        int[][] height = getHeight(matrix);
        Stack<Integer> st = new Stack<Integer>();
        int result = 0;
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j <= matrix[0].length; j++) {
                int cur = (j == matrix[0].length ? - 1: height[i][j]);
                while (!st.empty() && height[i][st.peek()] >= cur) {
                    int l = height[i][st.pop()];
                    int w = st.empty() ? j: j - st.peek() - 1;  
                    result = Math.max(result, w * l);  
                }
                st.push(j);
            }
            //when traverse over one row, remember to pop the last value out
            //or define the staci inside the second for loop
            st.pop();
        }
        return result;
    }
    
    int[][] getHeight(char[][] matrix) {
        int[][] height = new int[matrix.length][matrix[0].length];
        for (int i = 0; i < matrix[0].length; i++) {
            height[0][i] = matrix[0][i] - '0';
        }
        for (int i = 1; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (matrix[i][j] - '0'== 0) {
                    height[i][j] = 0;
                } else {
                    height[i][j] = height[i - 1][j] + 1;
                }
            }
        }
        return height;
    }
}