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

/**
 * 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.length!=in.length || pre.length==0 || in.length==0){
            return null;
        }
        TreeNode root = new TreeNode(pre[0]);
        int i = 0;
        while(in[i] != pre[0]){
            i++;
        }
        int[] preLeft = new int[i];
        int[] preRight = new int[pre.length-i-1];
        int[] inLeft = new int[i];
        int[] inRight = new int[pre.length-i-1];

        for(int j=0;j<pre.length;j++){
            if(j<i){
                preLeft[j] = pre[j+1];
                inLeft[j] = in[j];
            }else if(j>i){
                preRight[j-i-1] = pre[j];
                inRight[j-i-1] = in[j];
            }
        }
        root.left = reConstructBinaryTree(preLeft,inLeft);
        root.right = reConstructBinaryTree(preRight,inRight);

        return root;
    }
}