Decode the Coding Interview in C++: Real-World Examples/

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Invert Binary Tree

Invert Binary Tree

Understand and solve the interview question "Invert Binary Tree".

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Description

In this lesson, your task is to invert a given binary tree, T.

Let’s look at an example below:

Coding exercise

main.cpp
TreeNode.h
#include "TreeNode.h"
TreeNode* invertTree(TreeNode* root) {
    return root;
}
Invert binary tree

Solution

We can solve this problem using depth-first search (DFS).

The inverse of an empty tree is the empty tree. To invert tree T with root and subtrees left and right, we keep root the same and invert the right and left subtrees.

Let’s review the implementation below:

main.cpp
TreeNode.h
TreeNode* invertTree(TreeNode* root) {
    if (root == nullptr) {
        return root;
    }
    TreeNode* right = invertTree(root->right);
    TreeNode* left = invertTree(root->left);
    root->left = right;
    root->right = left;
    return root;
}
int main(){
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);
    root->right->left = new TreeNode(6);
    root->right->right = new TreeNode(7);
    auto res = invertTree(root);
    print(root);
    return 0;
}
Invert binary tree

Complexity measures

Time complexity Space complexity
O(n)O(n)
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