?區間x0到x1和區間y0到y1都是左閉右開的
解題基本思路是先判斷當前矩陣是不是全0或全1，如果是就直接返回新建的一個節點值(矩陣的統一值，葉子節點）,如果不是那就新建一個節點值，非葉并且左上右上左下右下四個方向上遞歸創建節點
/*
// Definition for a QuadTree node.
class Node {public boolean val;public boolean isLeaf;public Node topLeft;public Node topRight;public Node bottomLeft;public Node bottomRight;public Node() {this.val = false;this.isLeaf = false;this.topLeft = null;this.topRight = null;this.bottomLeft = null;this.bottomRight = null;}public Node(boolean val, boolean isLeaf) {this.val = val;this.isLeaf = isLeaf;this.topLeft = null;this.topRight = null;this.bottomLeft = null;this.bottomRight = null;}public Node(boolean val, boolean isLeaf, Node topLeft, Node topRight, Node bottomLeft, Node bottomRight) {this.val = val;this.isLeaf = isLeaf;this.topLeft = topLeft;this.topRight = topRight;this.bottomLeft = bottomLeft;this.bottomRight = bottomRight;}
}
*/class Solution {private Node construct(int[][] grid, int x0, int y0, int x1, int y1) {for (int i = x0; i < x1; i++)for (int j = y0; j < y1; j++)if (grid[i][j] != grid[x0][y0])return new Node(true, false,construct(grid, x0, y0, (x0 + x1) / 2, (y0 + y1) / 2),construct(grid, x0, (y0 + y1) / 2, (x0 + x1) / 2, y1),construct(grid, (x0 + x1) / 2, y0, x1, (y0 + y1) / 2),construct(grid, (x0 + x1) / 2, (y0 + y1) / 2, x1, y1));return new Node(grid[x0][y0] == 1, true);}public Node construct(int[][] grid) {return construct(grid, 0, 0, grid.length, grid.length);}
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)
)
