【力扣Hot100】刷题日记

海梨花2025-10-27 15:03

D32

二叉树的右视图

DFS

java 复制代码

/**
 * 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<Integer> list = new ArrayList<>();
    public List<Integer> rightSideView(TreeNode root) {
        
        dfs(root, 1);
        return list;
    }

    public void dfs(TreeNode root, int height){
        if(root == null) return;
        if(height > list.size()) list.add(root.val);
        dfs(root.right, height + 1);
        dfs(root.left, height + 1);
    }
}

BFS

java 复制代码

/**
 * 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<Integer> list = new ArrayList<>();
    Queue<TreeNode> queue = new ArrayDeque<>();
    public List<Integer> rightSideView(TreeNode root) {
        if(root != null) queue.add(root);
        bfs(root);
        return list;
    }

    public void bfs(TreeNode root){
        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i = 0; i < size; i++){
                // 层序遍历，但只留最右一个节点
                TreeNode node = queue.poll();
                if(node.left != null) queue.add(node.left);
                if(node.right != null) queue.add(node.right);
                if(i == size - 1) list.add(node.val);
            }
            
        }
    }
}