茕&茕 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。

 

代码实现（Java）

 

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        if(pre==null || in==null){
            return null;
        }
        if(pre.length!=in.length){
            System.out.println("长度不一样，非法输入");
        }
        return reConBTree(pre,0,pre.length-1,in,0,in.length-1);
    }
    public TreeNode reConBTree(int[] pre,int preLeft,int preRight,int[] in,int inLeft,int inRight){
        if(preLeft>preRight || inLeft>inRight){
            return null;
        }
        TreeNode root=new TreeNode(pre[preLeft]);
        for(int i=inLeft;i<=inRight;i++){
            if(pre[preLeft]==in[i]){
                root.left=reConBTree(pre,preLeft+1,preLeft+i-inRight,in,inLeft,i-1);
                root.right=reConBTree(pre,preLeft+i-inRight+1,preRight,in,i+1,inRight);
            }
        }
        return root;
    }
}