872. Leaf-Similar Trees

1. Description

Consider all the leaves of a binary tree, from left to right order, the values of those leaves form a leaf value sequence.

For example, in the given tree above, the leaf value sequence is (6, 7, 4, 9, 8).
Two binary trees are considered leaf-similar if their leaf value sequence is the same.
Return true if and only if the two given trees with head nodes root1 and root2 are leaf-similar.

2. Example

Example 1

Input: root1 = [3,5,1,6,2,9,8,null,null,7,4], root2 = [3,5,1,6,7,4,2,null,null,null,null,null,null,9,8]
Output: true

Example 2

Input: root1 = [1,2,3], root2 = [1,3,2]
Output: false

3. Constraints

• The number of nodes in each tree will be in the range [1, 200].
• Both of the given trees will have values in the range [0, 200].

4. Solutions

Depth-First Search

m is the number of nodes in root1, n is the number of nodes in root2
Time complexity: O(m + n)
Space complexity: O(m + n)

class Solution {
public:
    bool leafSimilar(TreeNode *root1, TreeNode *root2) {
        vector<int> leaf_nodes1, leaf_nodes2;

        save_leaf_nodes(root1, leaf_nodes1);
        save_leaf_nodes(root2, leaf_nodes2);
        return leaf_nodes1 == leaf_nodes2;
    }

private:
    void save_leaf_nodes(TreeNode *root, vector<int> &leaf_nodes) {
        if (root != nullptr) {
            if (root->left == nullptr && root->right == nullptr) {
                leaf_nodes.push_back(root->val);
            }

            save_leaf_nodes(root->left, leaf_nodes);
            save_leaf_nodes(root->right, leaf_nodes);
        }
    }
};