Java面试：重建二叉树题目

Posted 2023-01-03

题目：输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。

解答：

public static void main(String[] args) 
        //前序遍历数
        int [] preNode =1,2,4,7,3,5,6,8;
        //中序遍历数
        int [] infixNode =4,7,2,1,5,3,8,6;

        TreeNode treeNode = rebuildTree(preNode, infixNode);

        System.out.println(treeNode);

    

    private static TreeNode rebuildTree(int [] preNode,int [] infixNode)
            if(null == preNode|| null == infixNode || preNode.length ==0 ||
                    infixNode.length ==0 || preNode.length != infixNode.length)
                return null;
            
            TreeNode treeNode = new TreeNode(preNode[0]);
            for(int i =0 ; i < preNode.length ; i++)
                treeNode.leftNode= rebuildTree(Arrays.copyOfRange(preNode,1,i+1),Arrays.copyOfRange(infixNode,0,i));
                treeNode.rightNode =rebuildTree(Arrays.copyOfRange(preNode,i+1,preNode.length),Arrays.copyOfRange(infixNode,i+1,infixNode.length));
            
            return treeNode;
    

TreeNode类如下：

public class TreeNode 
    private  int value;

    TreeNode leftNode;

    TreeNode rightNode;

    public TreeNode(int value) 
        this.value = value;
    


    @Override
    public String toString() 
        return "TreeNode" +
                "value=" + value +
                ", leftNode=" + leftNode +
                ", rightNode=" + rightNode +
                ;