LC.P1110[删点成林]

方法一：DFS

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    List<TreeNode> ans = new ArrayList<>();
    boolean[] s = new boolean[1001];

    public List<TreeNode> delNodes(TreeNode root, int[] to_delete) {
        for (int x : to_delete) s[x] = true;
        if (dfs(root) != null) ans.add(root);
        return ans;
    }

    private TreeNode dfs(TreeNode node) {
        if (node == null) return null;
        node.left = dfs(node.left);
        node.right = dfs(node.right);
        if (!s[node.val]) return node;
        if (node.left != null) ans.add(node.left);
        if (node.right != null) ans.add(node.right);
        return null;
    }
}
  • 时间复杂度：$O(n + m)$，其中$n,m$分别是树的节点数和数组$toDelete$的大小
  • 空间复杂度：$O(n + m)$