题解 | #输出二叉树的右视图#

using System;
using System.Collections.Generic;


class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 求二叉树的右视图
     * @param preOrder int整型一维数组 先序遍历
     * @param inOrder int整型一维数组 中序遍历
     * @return int整型一维数组
     */
    List<int> preOrder;
    Dictionary<int, int> dicInOrder = new Dictionary<int, int>();
    public List<int> solve (List<int> preOrder, List<int> inOrder) {
        List<int> res = new List<int>();
        if(preOrder == null) return res;
        this.preOrder = preOrder;
        for(int i = 0; i < inOrder.Count; i++){
            dicInOrder.Add(inOrder[i], i);
        }
        TreeNode root = solveGetTree(0, 0, preOrder.Count - 1);
        Queue<TreeNode> que = new Queue<TreeNode>();
        que.Enqueue(root);
        while(que.Count != 0){
            for(int i = que.Count; i > 0; i--){
                TreeNode cur = que.Dequeue();
                if(cur.left != null) que.Enqueue(cur.left);
                if(cur.right != null) que.Enqueue(cur.right);
                if(i == 1) res.Add(cur.val);
            }
        }
        return res;
    }
    public TreeNode solveGetTree(int root, int left, int right){
        if(left > right) return null;
        TreeNode newNode = new TreeNode(preOrder[root]);
        int mid = dicInOrder[preOrder[root]];
        newNode.left = solveGetTree(root + 1, left, mid - 1);
        newNode.right = solveGetTree(root + mid - left + 1, mid + 1, right);
        return newNode;
    }
}