04重建二叉树--剑指offer，java版

04重建二叉树–剑指offer，java版

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

/**
 * 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<=0||in.length<=0||pre.length!=in.length){
             return null;
        }
        int len = pre.length;
        return ConstructCore(pre,in,0,len-1,0,len-1);
    }
    public TreeNode ConstructCore(int[] pre,int[] in,int preStart,int preEnd,int inStart,int inEnd){
        TreeNode root = new TreeNode(pre[preStart]);
        root.left = null;
        root.right = null;
        if(preStart == preEnd){
            if(inStart == inEnd && pre[preStart] == in[inStart]){
                return root;
            }else{
                System.out.println("wrong input");
                return null;
            }
        }
        int i = inStart;
        for(;i<inEnd;i++){
            if(in[i]==pre[preStart])
                break;
        }
        if(i == inEnd && in[i] != pre[preStart]){
            System.out.println("wrong input");
            return null;
        }
        int leftLen = i - inStart;
        if(leftLen > 0){
            root.left = ConstructCore(pre,in,preStart+1,preStart+leftLen,inStart,i-1);
        }
        if(inEnd - i > 0){
            root.right = ConstructCore(pre,in,preStart+leftLen+1,preEnd,i+1,inEnd);
        }
        return root;
        
    }

}