4.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。

题目解答

/**
 * 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) {
        TreeNode node=reConstructBinaryTree(pre,0,pre.length-1,in,0,in.length-1);
        return node;
    }
    private TreeNode reConstructBinaryTree(int [] pre,int startPre,int endPre,int [] in,int startIn,int endIn){
        if(startPre>endPre || startIn>endIn){
            return null;
        }
        TreeNode node=new TreeNode(pre[startPre]);
        for(int i=startIn;i<=endIn;i++){
            if(in[i]==pre[startPre]){
                node.left=reConstructBinaryTree(pre,startPre+1,startPre+i-startIn,in,startIn,i-1);
                node.right=reConstructBinaryTree(pre,startPre+i-startIn+1,endPre,in,i+1,endIn);
            }
        }
        return node;
    }
}