Populating Next Right Pointers in Each Node II

题目介绍

LeetCode 117. Populating Next Right Pointers in Each Node II。

复杂度

时间复杂度: O(n), 空间复杂度: O(n)

解题思路

public class Node {
    public var val: Int
    public var left: Node?
    public var right: Node?
    public var next: Node?
    public init(_ val: Int) {
        self.val = val
        self.left = nil
        self.right = nil
        self.next = nil
    }
}

class Solution {
    func connect(_ root: Node?) -> Node? {
        guard let root = root else {
            return nil
        }
        if root.left != nil {
            if root.right != nil {
                root.left!.next = root.right
            } else {
                // find next
                root.left!.next = findEmptyChild(root.next)
            }
        }
        if root.right != nil {
            // find next
            root.right!.next = findEmptyChild(root.next)
        }
        connect(root.right)
        connect(root.left)
        return root
    }

    private func findEmptyChild(_ node: Node?) -> Node? {
        if node == nil {
            return nil
        }
        if node?.left != nil {
            return node?.left
        }
        if node?.right != nil {
            return node?.right
        }
        return findEmptyChild(node?.next)
    }
}

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