4. 두 갈래 나무 재건

/**
 * 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) {
        TreeNode root = new TreeNode(pre[0]);
        int i = 0;
        while(in[i]!=root.val){
            i++;
        }
        if(i==0){
            root.left = null;
        }else{
            int [] leftPre = new int[i];
            System.arraycopy(pre,1,leftPre,0,i);
            int [] leftIn = new int[i];
            System.arraycopy(in,0,leftIn,0,i);
            root.left = reConstructBinaryTree(leftPre,leftIn);
            
        }
        
        if(i==in.length-1){
            root.right=null;
        }else{
            int [] rightPre = new int[pre.length-i-1];
            System.arraycopy(pre,i+1,rightPre,0,pre.length-i-1);
            int [] rightIn = new int[pre.length-i-1];
            System.arraycopy(in,i+1,rightIn,0,pre.length-i-1);
            root.right = reConstructBinaryTree(rightPre,rightIn);
        }

        return root;
    }
}

/**
 * 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){
            return null;
        }
        
        TreeNode root = new TreeNode(pre[0]);
        
        
        // 
        int rootIndex = -1;
        for(int i=0; i