题解 | 最大正方形

import java.util.Scanner;
import java.util.ArrayList;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        char[][] points = new char[n][n];

        // 遍历所有点
        for (int i = 0; i < n; i++)
        {
            String s = in.next();
            for (int j = 0; j < n; j++)
                points[i][j] = s.charAt(j);
        }

        int maxArea = -1;
        int x1 = 0, y1 = 0;
        int x2 = 0, y2 = 0;
        int x3 = 0, y3 = 0;
        int x4 = 0, y4 = 0;
        for (int x = 0; x < n; x++)
        {
            for (int y = 0; y < n; y++)
            {
                if (points[x][y] != '#') continue; // 寻找正方形的最左上的顶点

                for (int dx = 1; dx < n; dx++) // 往右找顶点
                {
                    for (int dy = 0; dy < n; dy++) // 往下找顶点
                    {
                        int area = dx * dx + dy * dy; //计算当前正方形的面积

                        if (area < maxArea) continue; // 面积小则不往下执行

                        // 利用左上方的顶点和向右向下的偏移量，计算剩下三个顶点的坐标
                        int x_2 = x + dx, y_2 = y + dy;
                        int x_3 = x + dx - dy, y_3 = y + dy + dx;
                        int x_4 = x - dy, y_4 = y + dx;

                        // 如果有顶点越界，则不符合条件，舍去
                        if (x_2 >= n || y_2 >= n || x_2 < 0 || y_2 < 0 ||
                            x_3 >= n || y_3 >= n || x_3 < 0 || y_3 < 0 ||
                            x_4 >= n || y_4 >= n || x_4 < 0 || y_4 < 0) continue;

                        // 如果顶点没越界，且三个顶点都是有效的（即为#）
                        if (points[x_2][y_2] == '#' &&
                            points[x_3][y_3] == '#' &&
                            points[x_4][y_4] == '#')
                        {
                            maxArea = area; // 最大面积换成当前更大的面积
                            // 更新四个顶点的坐标
                            x1 = x + 1; y1 = y + 1;
                            x2 = x_2 + 1; y2 = y_2 + 1;
                            x3 = x_3 + 1; y3 = y_3 + 1;
                            x4 = x_4 + 1; y4 = y_4 + 1;
                        }
                    }
                }
            }
        }

        System.out.println(x1 + " " + y1);
        System.out.println(x2 + " " + y2);
        System.out.println(x4 + " " + y4);
        System.out.println(x3 + " " + y3);
    }
}