872. Leaf-Similar Trees

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.

Note:

Both of the given trees will have between 1 and 100 nodes.

方法1: recursion

思路：

遍历两棵树，序列化所有叶节点之后比较是否一致。

易错点

1. 叶节点中间要用特殊符号拆开。

Complexity

Time complexity: O(T1 + T2)
Space complexity: O(T1 + T2)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool leafSimilar(TreeNode* root1, TreeNode* root2) {
        return leafHelper(root1, "") == leafHelper(root2, "");
    }
    
    string leafHelper(TreeNode* root, string t) {
        if (!root) return "";
        if (!root -> left && !root -> right) return to_string(root -> val) + "# ";
        return leafHelper(root -> left, t) + leafHelper(root -> right, t);
    }
};