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"title": "Construct Quad Tree",
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"content": "<p>Given a <code>n * n</code> matrix <code>grid</code> of <code>0's</code> and <code>1's</code> only. We want to represent the <code>grid</code> with a Quad-Tree.</p>\n\n<p>Return <em>the root of the Quad-Tree</em> representing the <code>grid</code>.</p>\n\n<p>Notice that you can assign the value of a node to <strong>True</strong> or <strong>False</strong> when <code>isLeaf</code> is <strong>False</strong>, and both are <strong>accepted</strong> in the answer.</p>\n\n<p>A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides, each node has two attributes:</p>\n\n<ul>\n\t<li><code>val</code>: True if the node represents a grid of 1's or False if the node represents a grid of 0's.</li>\n\t<li><code>isLeaf</code>: True if the node is leaf node on the tree or False if the node has the four children.</li>\n</ul>\n\n<pre>\nclass Node {\n public boolean val;\n public boolean isLeaf;\n public Node topLeft;\n public Node topRight;\n public Node bottomLeft;\n public Node bottomRight;\n}</pre>\n\n<p>We can construct a Quad-Tree from a two-dimensional area using the following steps:</p>\n\n<ol>\n\t<li>If the current grid has the same value (i.e all <code>1's</code> or all <code>0's</code>) set <code>isLeaf</code> True and set <code>val</code> to the value of the grid and set the four children to Null and stop.</li>\n\t<li>If the current grid has different values, set <code>isLeaf</code> to False and set <code>val</code> to any value and divide the current grid into four sub-grids as shown in the photo.</li>\n\t<li>Recurse for each of the children with the proper sub-grid.</li>\n</ol>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/11/new_top.png\" style=\"width: 777px; height: 181px;\" />\n<p>If you want to know more about the Quad-Tree, you can refer to the <a href=\"https://en.wikipedia.org/wiki/Quadtree\">wiki</a>.</p>\n\n<p><strong>Quad-Tree format:</strong></p>\n\n<p>The output represents the serialized format of a Quad-Tree using level order traversal, where <code>null</code> signifies a path terminator where no node exists below.</p>\n\n<p>It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list <code>[isLeaf, val]</code>.</p>\n\n<p>If the value of <code>isLeaf</code> or <code>val</code> is True we represent it as <strong>1</strong> in the list <code>[isLeaf, val]</code> and if the value of <code>isLeaf</code> or <code>val</code> is False we represent it as <strong>0</strong>.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/11/grid1.png\" style=\"width: 777px; height: 99px;\" />\n<pre>\n<strong>Input:</strong> grid = [[0,1],[1,0]]\n<strong>Output:</strong> [[0,1],[1,0],[1,1],[1,1],[1,0]]\n<strong>Explanation:</strong> The explanation of this example is shown below:\nNotice that 0 represnts False and 1 represents True in the photo representing the Quad-Tree.\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/12/e1tree.png\" style=\"width: 777px; height: 186px;\" />\n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<p><img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/12/e2mat.png\" style=\"width: 777px; height: 343px;\" /></p>\n\n<pre>\n<strong>Input:</strong> grid = [[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0],[1,1,1,1,1,1,1,1],[1,1,1,1,1,1,1,1],[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0]]\n<strong>Output:</strong> [[0,1],[1,1],[0,1],[1,1],[1,0],null,null,null,null,[1,0],[1,0],[1,1],[1,1]]\n<strong>Explanation:</strong> All values in the grid are not the same. We divide the grid into four sub-grids.\nThe topLeft, bottomLeft and bottomRight each has the same value.\nThe topRight have different values so we divide it into 4 sub-grids where each has the same value.\nExplanation is shown in the photo below:\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/12/e2tree.png\" style=\"width: 777px; height: 328px;\" />\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>n == grid.length == grid[i].length</code></li>\n\t<li><code>n == 2<sup>x</sup></code> where <code>0 <= x <= 6</code></li>\n</ul>\n",
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"code": "/*\n// Definition for a QuadTree node.\nclass Node {\npublic:\n bool val;\n bool isLeaf;\n Node* topLeft;\n Node* topRight;\n Node* bottomLeft;\n Node* bottomRight;\n \n Node() {\n val = false;\n isLeaf = false;\n topLeft = NULL;\n topRight = NULL;\n bottomLeft = NULL;\n bottomRight = NULL;\n }\n \n Node(bool _val, bool _isLeaf) {\n val = _val;\n isLeaf = _isLeaf;\n topLeft = NULL;\n topRight = NULL;\n bottomLeft = NULL;\n bottomRight = NULL;\n }\n \n Node(bool _val, bool _isLeaf, Node* _topLeft, Node* _topRight, Node* _bottomLeft, Node* _bottomRight) {\n val = _val;\n isLeaf = _isLeaf;\n topLeft = _topLeft;\n topRight = _topRight;\n bottomLeft = _bottomLeft;\n bottomRight = _bottomRight;\n }\n};\n*/\n\nclass Solution {\npublic:\n Node* construct(vector<vector<int>>& grid) {\n \n }\n};",
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"code": "/**\n * // Definition for a QuadTree node.\n * function Node(val,isLeaf,topLeft,topRight,bottomLeft,bottomRight) {\n * this.val = val;\n * this.isLeaf = isLeaf;\n * this.topLeft = topLeft;\n * this.topRight = topRight;\n * this.bottomLeft = bottomLeft;\n * this.bottomRight = bottomRight;\n * };\n */\n\n/**\n * @param {number[][]} grid\n * @return {Node}\n */\nvar construct = function(grid) {\n \n};",
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"code": "# Definition for a QuadTree node.\n# class Node\n# attr_accessor :val, :isLeaf, :topLeft, :topRight, :bottomLeft, :bottomRight\n# def initialize(val=false, isLeaf=false, topLeft=nil, topRight=nil, bottomLeft=nil, bottomRight=nil)\n# @val = val\n# @isLeaf = isLeaf\n# @topLeft = topLeft\n# @topRight = topRight\n# @bottomLeft = bottomLeft\n# @bottomRight = bottomRight\n# end\n# end\n\n# @param {Integer[][]} grid\n# @return {Node}\ndef construct(grid)\n\t\nend",
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