题解 | #重建二叉树#

import java.util.*;
/**
 * 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 [] vin) {
        return re2(pre,vin,pre.length);
    }
    public TreeNode re2(int [] pre,int [] vin,int len) {
        if(len<=0) return null;
        TreeNode T = new TreeNode(pre[0]);
        
        int i;
        for(i=0; i<len; i++)
            if(pre[0]==vin[i]) break;
        //根左右 左i根1右i+1
        T.left = re2(Arrays.copyOfRange(pre,1,i+1),Arrays.copyOfRange(vin,0,i),i);
        T.right = re2(Arrays.copyOfRange(pre,i+1,pre.length),Arrays.copyOfRange(vin,i+1,pre.length),len-i-1); 
        return T;
    }
}

知识点：数组的创建 由于不同于c，java无指针，所以要Arrays.copyOfRange(pre,1,i+1)，不能pre+1