leetcode讲解--872. Leaf-Similar Trees

题目

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.

讲解

这道题的思路很简单，先扫描出两个树的叶子结果集，然后比较就行了。考察点是树的遍历。递归的时候首先要判断结点是否为空。

Java代码

/**
 * 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);
    }
}