[Swift]LeetCode652. 寻找重复的子树 | Find Duplicate Subtrees

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Given a binary tree, return all duplicate subtrees. For each kind of duplicate subtrees, you only need to return the root node of any one of them.

Two trees are duplicate if they have the same structure with same node values.

Example 1:

        1
       / \
      2   3
     /   / \
    4   2   4
       /
      4

The following are two duplicate subtrees:

      2
     /
    4

and

    4

Therefore, you need to return above trees' root in the form of a list.

---

给定一棵二叉树，返回所有重复的子树。对于同一类的重复子树，你只需要返回其中任意一棵的根结点即可。

两棵树重复是指它们具有相同的结构以及相同的结点值。

示例 1：

        1
       / \
      2   3
     /   / \
    4   2   4
       /
      4

下面是两个重复的子树：

      2
     /
    4

和

    4

因此，你需要以列表的形式返回上述重复子树的根结点。

---

Runtime: 72 ms

Memory Usage: 26.2 MB

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        var res:[TreeNode?] = [TreeNode?]()
        var m:[String:Int] = [String:Int]()
        helper(root, &m, &res)
        return res
    }
    
    func helper(_ node: TreeNode?,_ m:inout [String:Int],_ res:inout [TreeNode?]) -> String
    {
        if node == nil {return "#"}
        var str:String = String(node!.val) + "," + helper(node!.left, &m, &res) + "," + helper(node!.right, &m, &res)
        if m[str] == 1
        {
            res.append(node)
        }
        m[str,default:0] += 1
        return str
    }
}

---

72ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        var map = [String: Int]()
        var result = [TreeNode?]()
        var inorderT = findDuplicateSubtrees(root, &map, &result)
        
        return result
    }
    
    func findDuplicateSubtrees(_ root: TreeNode?, _ map: inout [String: Int], _ result: inout [TreeNode?]) -> String {
        guard let root = root else { 
            return ""
        }
        
        var str = "("
        str += findDuplicateSubtrees(root.left, &map, &result)
        str += "\(root.val)"
        str += findDuplicateSubtrees(root.right, &map, &result)
        str += ")"
        
        map[str] = (map[str] ?? 0) + 1
        
        if map[str] == 2 {
            result.append(root)
        }
        
        return str                                
    }
}

---

72ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        var res:[TreeNode?] = [TreeNode?]()
        var m:[String:Int] = [String:Int]()
        helper(root, &m, &res)
        return res
    }
    
    func helper(_ node: TreeNode?,_ m:inout [String:Int],_ res:inout [TreeNode?]) -> String
    {
        if node == nil {return "#"}
        var str:String = String(node!.val) + "," + helper(node!.left, &m, &res) + "," + helper(node!.right, &m, &res)
        if m[str] == 1
        {
            res.append(node)
        }
        m[str,default:0] += 1
        return str
    }
}

---

88ms

class Solution {
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        var result = [TreeNode]()
        var dict = [String: Int]()
        helper(&result, &dict, root)
        return result
    }
    
    func helper(_ result: inout [TreeNode], _ dict: inout [String: Int], _ root: TreeNode?) -> String {
        guard let root = root else { return "#" }
        
        let left = helper(&result, &dict, root.left)
        let right = helper(&result, &dict, root.right)
        
        let s = "\(root.val)" + "," + left + "," + right        
        if let count = dict[s] {
            if count == 1 {
                result.append(root)
            }
            dict[s] = count + 1
        } else {
            dict[s] = 1
        }
        
        return s
    }
}

---

92ms

class Solution {
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        var subTree: [String: Int] = [:]
        var res: [TreeNode?] = []
        helper(root, &subTree, &res)
        return res
    }
    
    private func helper(_ root: TreeNode?, _ subTree: inout [String: Int], _ res: inout [TreeNode?]) -> String {
        guard let root = root else { return "#" }
        let serializedString = "\(String(root.val)) \(helper(root.left, &subTree, &res)) \(helper(root.right, &subTree, &res))"
        
        if let count = subTree[serializedString] {
            if count == 1 {
                res.append(root)
            }
            subTree[serializedString] = count + 1
        } else {
            subTree[serializedString] = 1
        }
        
        return serializedString
    }
}

---

96ms

class Solution {
    var foundSubtrees = Set<String>()
    var solution = [String: TreeNode]()
    
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        guard let root = root else { return [] }
        solve(root)
        return [TreeNode](solution.values)
    }
    
    func solve(_ node: TreeNode) -> String {
        let leftKey = node.left.map { return solve($0) } ?? "NL"
        let rightKey = node.right.map { return solve($0) } ?? "NR"
        let key = "[\(String(node.val))/\(leftKey):\(rightKey)]"
        if foundSubtrees.contains(key) {
            solution[key] = node
        } else {
            foundSubtrees.insert(key)
        }
        return key
    }
}

extension TreeNode: Hashable {
    public var hashValue: Int {
        return val
    }
    
    static public func == (lhs: TreeNode, rhs: TreeNode) -> Bool {
        return lhs.val == rhs.val
    }
}

---

100ms

class Solution {
    var res: [TreeNode?] = []
    var map: [String: Int] = [:]
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        preorder(root)
        return res
    }
    
    private func preorder(_ root: TreeNode?) -> String {
        
        guard let root = root else { return "#"}
        let serial = "\(root.val), \(preorder(root.left)), \(preorder(root.right))"
        if map[serial] == 1 { res.append(root) }
        
        map[serial, default: 0] += 1
        return serial
    }
}

---

104ms

class Solution {
    var ans = [TreeNode]()
    var subTrees = [String : Int]()
    
    func collect(node_: TreeNode?) -> String {
        guard let node = node_ else { return "#" }
        
        let serial = "\(node.val),\(collect(node_: node.left)),\(collect(node_: node.right))"
        
        if let count = subTrees[serial] {
            subTrees[serial] = count + 1
            if count + 1 == 2 {
                ans.append(node)
            }
        } else {
            subTrees[serial] = 1
        }
        return serial
        
    }
    
    
    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
        collect(node_: root)
        return ans
    }
}