P85_Maximal_Rectangle.java

package solution.hard;

import java.util.Arrays;

/**
 * @author Yi-Lo
 * 2020/12/10 17:14
 * @version 1.0
 * @topics Stack、Array、Hash Table、Dynamic Programming
 * @urllink https://leetcode-cn.com/problems/maximal-rectangle/
 */
public class P85_Maximal_Rectangle {

    public static int maximalRectangle(char[][] matrix) {
        if (matrix.length == 0) return 0;
        int m = matrix.length, n = matrix[0].length;
        int[] left = new int[n];
        int[] right = new int[n];
        int[] height = new int[n];
        Arrays.fill(right, n);
        int maxArea = 0;
        for (int i = 0; i < m; i++) {
            int cur_left = 0, cur_right = n;
            // update height
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == '1') height[j]++;
                else height[j] = 0;
            }
            // update left
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == '1') {
                    left[j] = Math.max(left[j], cur_left);
                } else {
                    left[j] = 0;
                    cur_left = j + 1;
                }
            }
            // update right
            for (int j = n - 1; j >= 0; j--) {
                if (matrix[i][j] == '1') {
                    right[j] = Math.min(right[j], cur_right);
                } else {
                    right[j] = n;
                    cur_right = j;
                }
            }
            // update area
            for (int j = 0; j < n; j++) {
                maxArea = Math.max(maxArea, (right[j] - left[j]) * height[j]);
            }
        }
        return maxArea;
    }

    public static void main(String[] args) {
        char[][] matrix = {{'1', '0', '1', '0', '0'}, {'1', '0', '1', '1', '1'}, {'1', '1', '1', '1', '1'}, {'1', '0', '0', '1', '0'}};
        System.out.println(maximalRectangle(matrix));
    }
}