algorithms/leetcode/226-InvertBinaryTree.go at master · freewu/algorithms · GitHub

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package main

// 226. Invert Binary Tree
// Given the root of a binary tree, invert the tree, and return its root.

// Example 1:
// <img src="https://assets.leetcode.com/uploads/2021/03/14/invert1-tree.jpg" />
// Input: root = [4,2,7,1,3,6,9]
// Output: [4,7,2,9,6,3,1]

// Example 2:
// <img src="https://assets.leetcode.com/uploads/2021/03/14/invert2-tree.jpg" />
// Input: root = [2,1,3]
// Output: [2,3,1]

// Example 3:
// Input: root = []
// Output: []

// Constraints:
//     The number of nodes in the tree is in the range [0, 100].
//     -100 <= Node.val <= 100

import "fmt"

// Definition for a binary tree node.
type TreeNode struct {
    Val int
    Left *TreeNode
    Right *TreeNode
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
// dfs
func invertTree(root *TreeNode) *TreeNode {
    if root == nil {
        return nil
    }
    // General cases:
    // invert child node of current root
    root.Left, root.Right = root.Right, root.Left
    // invert subtree with DFS
    invertTree(root.Left)
    invertTree(root.Right)
    return root
}

func invertTree1(root *TreeNode) *TreeNode {
    if root == nil{
        return nil
    }
    root.Left, root.Right = invertTree1(root.Right), invertTree1(root.Left)
    return root
}

func main() {
    // Example 1:
    // <img src="https://assets.leetcode.com/uploads/2021/03/14/invert1-tree.jpg" />
    // Input: root = [4,2,7,1,3,6,9]
    // Output: [4,7,2,9,6,3,1]
    tree1 := &TreeNode {
        4,
        &TreeNode { 2, &TreeNode{1, nil, nil}, &TreeNode{3, nil, nil}, },
        &TreeNode { 7, &TreeNode{6, nil, nil}, &TreeNode{9, nil, nil}, },
    }
    fmt.Println(invertTree(tree1))
    // Example 2:
    // <img src="https://assets.leetcode.com/uploads/2021/03/14/invert2-tree.jpg" />
    // Input: root = [2,1,3]
    // Output: [2,3,1]
    tree2 := &TreeNode {
        2,
        &TreeNode{1, nil, nil},
        &TreeNode{3, nil, nil},
    }
    fmt.Println(invertTree(tree2))

    tree11 := &TreeNode{
        4,
        &TreeNode { 2, &TreeNode{1, nil, nil}, &TreeNode{3, nil, nil}, },
        &TreeNode { 7, &TreeNode{6, nil, nil}, &TreeNode{9, nil, nil}, },
    }
    fmt.Println(invertTree1(tree11))
    tree12 := &TreeNode{
        2,
        &TreeNode{1, nil, nil},
        &TreeNode{3, nil, nil},
    }
    fmt.Println(invertTree1(tree12))
}