README_EN.md

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true	Medium	https://github.com/doocs/leetcode/edit/main/solution/1600-1699/1666.Change%20the%20Root%20of%20a%20Binary%20Tree/README_EN.md	Tree Depth-First Search Binary Tree

1666. Change the Root of a Binary Tree 🔒

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Description

Given the root of a binary tree and a leaf node, reroot the tree so that the leaf is the new root.

You can reroot the tree with the following steps for each node cur on the path starting from the leaf up to the root​​​ excluding the root:

1. If cur has a left child, then that child becomes cur's right child.
2. cur's original parent becomes cur's left child. Note that in this process the original parent's pointer to cur becomes null, making it have at most one child.

Return the new root of the rerooted tree.

Note: Ensure that your solution sets the Node.parent pointers correctly after rerooting or you will receive "Wrong Answer".

 

Example 1:

Input: root = [3,5,1,6,2,0,8,null,null,7,4], leaf = 7
Output: [7,2,null,5,4,3,6,null,null,null,1,null,null,0,8]

Example 2:

Input: root = [3,5,1,6,2,0,8,null,null,7,4], leaf = 0
Output: [0,1,null,3,8,5,null,null,null,6,2,null,null,7,4]

 

Constraints:

• The number of nodes in the tree is in the range [2, 100].
• -109 <= Node.val <= 109
• All Node.val are unique.
• leaf exist in the tree.

Solutions

Solution 1

Python3

"""
# Definition for a Node.
class Node:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None
        self.parent = None
"""


class Solution:
    def flipBinaryTree(self, root: "Node", leaf: "Node") -> "Node":
        cur = leaf
        p = cur.parent
        while cur != root:
            gp = p.parent
            if cur.left:
                cur.right = cur.left
            cur.left = p
            p.parent = cur
            if p.left == cur:
                p.left = None
            elif p.right == cur:
                p.right = None
            cur = p
            p = gp
        leaf.parent = None
        return leaf

Java

/*
// Definition for a Node.
class Node {
    public int val;
    public Node left;
    public Node right;
    public Node parent;
};
*/

class Solution {
    public Node flipBinaryTree(Node root, Node leaf) {
        Node cur = leaf;
        Node p = cur.parent;
        while (cur != root) {
            Node gp = p.parent;
            if (cur.left != null) {
                cur.right = cur.left;
            }
            cur.left = p;
            p.parent = cur;
            if (p.left == cur) {
                p.left = null;
            } else if (p.right == cur) {
                p.right = null;
            }
            cur = p;
            p = gp;
        }
        leaf.parent = null;
        return leaf;
    }
}

C++

/*
// Definition for a Node->
class Node {
public:
    int val;
    Node* left;
    Node* right;
    Node* parent;
};
*/

class Solution {
public:
    Node* flipBinaryTree(Node* root, Node* leaf) {
        Node* cur = leaf;
        Node* p = cur->parent;
        while (cur != root) {
            Node* gp = p->parent;
            if (cur->left) {
                cur->right = cur->left;
            }
            cur->left = p;
            p->parent = cur;
            if (p->left == cur) {
                p->left = nullptr;
            } else if (p->right == cur) {
                p->right = nullptr;
            }
            cur = p;
            p = gp;
        }
        leaf->parent = nullptr;
        return leaf;
    }
};

JavaScript

/**
 * // Definition for a Node.
 * function Node(val) {
 *    this.val = val;
 *    this.left = null;
 *    this.right = null;
 *    this.parent = null;
 * };
 */

/**
 * @param {Node} node
 * @return {Node}
 */
var flipBinaryTree = function (root, leaf) {
    let cur = leaf;
    let p = cur.parent;
    while (cur != root) {
        const gp = p.parent;
        if (cur.left != null) {
            cur.right = cur.left;
        }
        cur.left = p;
        p.parent = cur;
        if (p.left == cur) {
            p.left = null;
        } else if (p.right == cur) {
            p.right = null;
        }
        cur = p;
        p = gp;
    }
    leaf.parent = null;
    return leaf;
};

C#

/*
// Definition for a Node.
public class Node {
    public int val;
    public Node left;
    public Node right;
    public Node parent;
}
*/

public class Solution {
    public Node FlipBinaryTree(Node root, Node leaf) {
        Node cur = leaf;
        Node p = cur.parent;
        while (cur != root) {
            Node gp = p.parent;
            if (cur.left != null) {
                cur.right = cur.left;
            }
            cur.left = p;
            p.parent = cur;
            if (p.left == cur) {
                p.left = null;
            } else if (p.right == cur) {
                p.right = null;
            }
            cur = p;
            p = gp;
        }
        leaf.parent = null;
        return leaf;
    }
}