题解 | #重建二叉树#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param preOrder int整型一维数组 
     * @param vinOrder int整型一维数组 
     * @return TreeNode类
     */
    public TreeNode reConstructBinaryTree (int[] preOrder, int[] vinOrder) {
        // write code here
        //前序遍历 1,2,4,7,3,5,6,8  //4,7,2,1,5,3,8,6第一个节点为根节点
        if(preOrder.length==0||vinOrder.length==0){
            return null;
        }
        int root=preOrder[0];//根节点
        TreeNode r=new TreeNode(root);
        //去中序遍历里面找到该值
        int rIndex=0;
        for(int i=0;i<vinOrder.length;i++){
            if(vinOrder[i]==root){
                rIndex=i;
            }
        }
        //左边元素个数为rIndex,右边元素为len-rIndex
        int[] preLeft=Arrays.copyOfRange(preOrder,1,rIndex+1);
        int[] preRight=Arrays.copyOfRange(preOrder,rIndex+1,preOrder.length);
        int[] inLeft=Arrays.copyOfRange(vinOrder,0,rIndex);
        int[] inRight=Arrays.copyOfRange(vinOrder,rIndex+1,vinOrder.length);
        r.left=reConstructBinaryTree(preLeft,inLeft);
        r.right=reConstructBinaryTree(preRight,inRight);
        return r;
    }
}