二叉树的右透视图

思路如下借助二叉树的层次遍历用两个队列一个队列存当前遍历的层另一个队列存下一层。当前队列是最后一个节点的时候最后这个节点就是右透视图需要展示的节点。在遍历当前队列的时候把下一层加入下一层队列。处理完当前层队列后把下一层设置成当前层然后重复上面的步骤。/**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 {public List rightSideView(TreeNode root) {List result new ArrayList();if (root null) {return result;}Queue currentLevel new ArrayDeque();Queue nextLevel new ArrayDeque();currentLevel.add(root);while (!currentLevel.isEmpty()) {TreeNode node currentLevel.poll();if (node.left ! null) { nextLevel.add(node.left); } if (node.right ! null) { nextLevel.add(node.right); } if (currentLevel.isEmpty()) { QueueTreeNode temp currentLevel; currentLevel nextLevel; nextLevel temp; result.add(node.val); } } return result; }}