題目

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.

講解

這道題的思路很簡單，先掃描出兩個樹的葉子結果集，然后比較就行了。考察點是樹的遍歷。遞歸的時候首先要判斷結點是否為空。

Java代碼

/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/ class Solution {public boolean leafSimilar(TreeNode root1, TreeNode root2) {List<Integer> leaves1 = new ArrayList<>();List<Integer> leaves2 = new ArrayList<>();getLeaves(root1, leaves1);getLeaves(root2, leaves2);if(leaves1.size()!=leaves2.size()){return false;}else{for(int i=0;i<leaves1.size();i++){if(leaves1.get(i)!=leaves2.get(i)){return false;}}}return true;}private void getLeaves(TreeNode root, List<Integer> leaves){if(root==null){return;}if(root.left==null && root.right==null){leaves.add(root.val);return;}getLeaves(root.left, leaves);getLeaves(root.right, leaves);} }

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