剑指offer-重建二叉树

题目描述

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。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

 

根据前序遍历序列找到子树根节点，并在中序遍历序列中找到该点，以分割左右子树的序列

public class Solution {//树 my
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        return reConBTreeIndex(pre,0,pre.length-1,in,0,in.length-1);
    }
    private TreeNode reConBTreeIndex(int[] pre,int preLeft,int preRight,int[] in,int inLeft,int inRight){
        if(preRight<preLeft||inLeft>inRight){
            return null;
        }
        else{
            //System.out.println(pre[preLeft]+"--"+pre[preRight]+"   "+in[inLeft]+"--"+in[inRight]);
            TreeNode node = new TreeNode(pre[preLeft]);
            for (int i = inLeft; i <= inRight; i++) {
                if(in[i]==pre[preLeft]){
                    node.left = reConBTreeIndex(pre,preLeft+1,i-inLeft+preLeft,in,inLeft,i-1);
                    node.right = reConBTreeIndex(pre,preRight-inRight+i+1,preRight,in,i+1,inRight);
                }
            }
            return node;
        }
    }
}