[swift] LeetCode 102. Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},
3
/ \
9 20
/ \
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]

func levelOrder(_ root: TreeNode?) -> [[Int]] {
    guard let root = root else { return [] }

    var q = [TreeNode](), lists = [[Int]]()
    q.append(root)

    while !q.isEmpty {
        lists.append(q.map { $0.val })

        q = q.reduce([]) { l, t in
            l + [t.left, t.right]
            }.compactMap({$0})
    }

    return lists
}

func levelOrder(_ root: TreeNode?) -> [[Int]] {

guard let root = root else { return [] }

var q = [TreeNode](), lists = [[Int]]()

q.append(root)

while !q.isEmpty {

lists.append(q.map { $0.val })

q = q.reduce([]) { l, t in

l + [t.left, t.right]

}.compactMap({$0})

}

return lists

}

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