【力扣Hot100】刷题日记

D32

二叉树的右视图

二叉树的右视图

DFS

/*** 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

/*** 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);}}}
}