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; }
 * }
 */
    Map<Integer,Integer> map = new HashMap<>();
    public TreeNode reConstructBinaryTree(int [] pre,int [] vin) {
        if(pre == null||pre.length == 0){
            return null;
        }
        for(int i = 0;i<vin.length;i++){
            map.put(vin[i],i);
        }
        return binaryTree(pre,0,pre.length-1,vin,0,vin.length-1);
        
    public TreeNode binaryTree(int[] pre,int preLeft,int preRight,int[] vin,int vinLeft,int vinRight){
        if(preLeft > preRight){
            return null;
        }
        TreeNode root = new TreeNode(pre[preLeft]);
        int index = map.get(pre[preLeft]);
        int size = index-vinLeft;
        root.left = binaryTree(pre,preLeft+1,preLeft+size,vin,vinLeft,index-1);
        root.right = binaryTree(pre,preLeft+size+1,preRight,vin,index+1,vinRight);
        return root;
    }
}