814. Binary Tree Pruning（二叉树的修剪）

最新推荐文章于 2022-11-10 21:20:50 发布

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博客围绕二叉树问题展开，给定一个每个节点值为0或1的二叉树，要求移除其中所有不包含1的子树，并给出了该题的方法思路。

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题目描述

We are given the head node root of a binary tree, where additionally every node’s value is either a 0 or a 1.Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.
(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)
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方法思路

class Solution {
    //Runtime: 1 ms, faster than 100.00%
    //Memory Usage: 36.8 MB, less than 66.67%
    public TreeNode pruneTree(TreeNode root) {
        if(root == null) return root;
        if(!containsOne(root.left)) root.left = null;
        if(!containsOne(root.right)) root.right = null;
        pruneTree(root.left);
        pruneTree(root.right);
        return root;
    }
    public boolean containsOne(TreeNode root){
        if(root == null) 
            return false;
        if(root.left == null && root.right == null && root.val == 0)
            return false;
        if(root.val == 1)
            return true;
        return containsOne(root.left) || containsOne(root.right);
    }
}