872.Leaf-Similar Trees

QUESTION:

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

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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 100nodes.

EXPLANATION:

看到题目就知道其实是一个中序遍历，但是要剔除不是leaf的节点。那么怎么才能算不是leaf的节点呢，就是node.left和node.right都不为null。

这样其实就可以了。

SOLUTION:

class Solution {
    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        ArrayList<Integer> values1 = new ArrayList<>();
        ArrayList<Integer> values2 = new ArrayList<>();
        leafSimilarHelper(root1,values1);
        leafSimilarHelper(root2,values2);
        for(int i = 0;i<values1.size();i++){
            if(i<values2.size()){
                if(values1.get(i)!=values2.get(i)) return false;
            }else return false;
        }
        return true;
    }
    
    
    public static void leafSimilarHelper(TreeNode root,ArrayList list){
        if(root == null) return;
        leafSimilarHelper(root.left,list);
        if(root.left==null && root.right==null) list.add(root.val);
        leafSimilarHelper(root.right,list);
    }
}
>
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