dev/democards/problems/problems/236.lowest-common-ancestor-of-a-binary-tree.ipynb

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    "Given a binary tree, find the lowest common ancestor (LCA) of two given nodes\n",
    "in the tree.\n",
    "\n",
    "According to the [definition of LCA on\n",
    "Wikipedia](https://en.wikipedia.org/wiki/Lowest_common_ancestor): \"The lowest\n",
    "common ancestor is defined between two nodes p and q as the lowest node in T\n",
    "that has both p and q as descendants (where we allow **a node to be a\n",
    "descendant of itself** ).\"\n",
    "\n",
    "\n",
    "\n",
    "**Example 1:**\n",
    "\n",
    "![](https://assets.leetcode.com/uploads/2018/12/14/binarytree.png)\n",
    "\n",
    "\n",
    "\n",
    "    Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1\n",
    "    Output: 3\n",
    "    Explanation: The LCA of nodes 5 and 1 is 3.\n",
    "\n",
    "\n",
    "**Example 2:**\n",
    "\n",
    "![](https://assets.leetcode.com/uploads/2018/12/14/binarytree.png)\n",
    "\n",
    "\n",
    "\n",
    "    Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4\n",
    "    Output: 5\n",
    "    Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.\n",
    "\n",
    "\n",
    "**Example 3:**\n",
    "\n",
    "\n",
    "\n",
    "    Input: root = [1,2], p = 1, q = 2\n",
    "    Output: 1\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Constraints:**\n",
    "\n",
    "  * The number of nodes in the tree is in the range `[2, 105]`.\n",
    "  * `-109 <= Node.val <= 109`\n",
    "  * All `Node.val` are **unique**.\n",
    "  * `p != q`\n",
    "  * `p` and `q` will exist in the tree."
   ],
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    {
     "output_type": "execute_result",
     "data": {
      "text/plain": "lowest_common_ancestor_236 (generic function with 1 method)"
     },
     "metadata": {},
     "execution_count": 1
    }
   ],
   "cell_type": "code",
   "source": [
    "# @lc code=start\n",
    "using LeetCode\n",
    "\n",
    "function lowest_common_ancestor_236(\n",
    "    root::TreeNode{Int}, p::TreeNode{Int}, q::TreeNode{Int}\n",
    ")::TreeNode{Int}\n",
    "    function dfs(node::Union{TreeNode{Int},Nothing})\n",
    "        (isnothing(node) || node == p || node == q) && return node\n",
    "        left, right = dfs(node.left), dfs(node.right)\n",
    "        isnothing(left) && isnothing(right) && return nothing\n",
    "        !isnothing(left) && !isnothing(right) && return node\n",
    "        return !isnothing(left) ? left : right\n",
    "    end\n",
    "    return dfs(root)\n",
    "end\n",
    "# @lc code=end"
   ],
   "metadata": {},
   "execution_count": 1
  },
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   "source": [
    "---\n",
    "\n",
    "*This notebook was generated using [Literate.jl](https://github.com/fredrikekre/Literate.jl).*"
   ],
   "metadata": {}
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