题解 | #输出二叉树的右视图#

import java.util.*;


public 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
     */
    public int[] solve (int[] preOrder, int[] inOrder) {
        // write code here
        // 解题思路：1.重建二叉树。2.二叉树层序遍历
        TreeNode root =  buildTree( preOrder,  inOrder);
        List<Integer> rightList = rightView( root);

        int[] rightArray = new int[rightList.size()];

        for (int i = 0; i < rightList.size(); i++) {
            rightArray[i] = rightList.get(i);
        }

        return rightArray;
    }

    private List<Integer> rightView(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(root);

        List<Integer> rightList = new ArrayList<>();

        while (!queue.isEmpty()) {
            int l = queue.size();
            int v = 0;
            for (int i = 0; i < l; i++) {
                TreeNode node = queue.poll();
                v = node.val;

                if (node.left != null) {
                    queue.add(node.left);
                }

                if (node.right != null) {
                    queue.add(node.right);
                }
            }
            rightList.add(v);
        }

        return rightList;
    }

    private TreeNode buildTree(int[] preOrder, int[] inOrder) {

        if (preOrder == null || inOrder == null || preOrder.length == 0) {
            return null;
        }

        int rootValue = preOrder[0];
        int pos = 0;
        TreeNode root = new TreeNode(rootValue);

        if (preOrder.length == 1 || inOrder.length == 1) {
            return root;
        }

        for (int i = 0; i < inOrder.length; i++) {
            if (rootValue == inOrder[i]) {
                pos = i;
                break;
            }
        }

        root.left =  buildTree(Arrays.copyOfRange(preOrder, 1, pos + 1),
                               Arrays.copyOfRange(inOrder, 0, pos));
        root.right = buildTree(Arrays.copyOfRange(preOrder,  pos + 1,
                               preOrder.length),
                               Arrays.copyOfRange(inOrder, pos + 1,  inOrder.length));

        return root;
    }
}