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) {
        TreeNode treeNode = buildTree(preOrder, inOrder);

        List<Integer> list = new LinkedList<>();
        Queue<TreeNode> query = new LinkedList<>();
        query.add(treeNode);
        while (!query.isEmpty()) {
            int size = query.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = query.poll();
                if (node != null && node.left != null) {
                    query.add(node.left);
                }
                if (node != null && node.right != null) {
                    query.add(node.right);
                }
                if (i == size - 1) {
                    if (node != null) {
                        list.add(node.val);
                    }
                }
            }
        }
        int[] ans = new int[list.size()];
        for (int i = 0; i < list.size(); i++) {
            ans[i] = list.get(i);
        }
        return ans;
    }


    static public TreeNode buildTree(int[] preOrder, int[] inOrder) {
        TreeNode root = new TreeNode(preOrder[0]);
        if (preOrder.length == 1) {
            return root;
        }
        int index = 0;
        for (int i = 1; i < inOrder.length; i++) {
            if (inOrder[i] == preOrder[0]) {
                index = i;
                break;
            }
        }
        int[] leftPreOrder = new int[index];
        int[] rightPreOrder = new int[preOrder.length - index - 1];
        System.arraycopy(preOrder, 1, leftPreOrder, 0, index);

        for (int i = index + 1; i < inOrder.length; i++) {
            rightPreOrder[i - index - 1] = preOrder[i];
        }

        int[] leftInOrder = new int[index];
        int[] rightInOrder = new int[inOrder.length - index - 1];

        System.arraycopy(inOrder, 0, leftInOrder, 0, index);
        for (int j = index + 1; j < inOrder.length; j++) {
            rightInOrder[j - index - 1] = inOrder[j];
        }
        if (leftPreOrder.length > 0) {
            root.left = buildTree(leftPreOrder, leftInOrder);
        }
        if (rightPreOrder.length > 0) {
            root.right = buildTree(rightPreOrder, rightInOrder);
        }
        return root;
    }
}