트리 - 중간 순서와 앞 순서, 중간 순서와 뒤 순서로 두 갈래 트리 재구성

/**
 * 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==null||in==null||pre.length!=in.length)
            return null;
        return  helper(pre,0,pre.length-1,in,0,in.length-1);
        
    }
    public TreeNode helper(int []pre,int prelow,int prehigh,int[] in,int inlow,int inhigh)
        {
        if(prelow>prehigh||inlow>inhigh)
            return null;
        TreeNode root=new TreeNode(pre[prelow]);
        int i=inlow;
        for(;i<inhigh&&in[i]!=root.val;i++);
        
            root.left=helper(pre,prelow+1,prelow+i-inlow,in,inlow,i-1);// ；
        
            root.right=helper(pre,prelow+i-inlow+1,prehigh,in,i+1,inhigh);
        
        return root;
    }
}

public class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
       if(inorder == null||postorder == null||inorder.length == 0||inorder.length!=postorder.length)
           return null;
        return build_Tree(inorder,0,inorder.length-1,postorder,0,postorder.length-1);         
    }
    
    public TreeNode build_Tree(int[] inorder,int inbegin,int inend,int[] postorder,int postbegin,int postend)
        {
        if(inbegin>inend||postbegin>postend)
            return null;
        
        int root_val=postorder[postend];
        
        TreeNode root=new TreeNode(root_val);
        
        int index=inbegin;
        for(;inorder[index]!=root_val;index++)
            {   
        }
        // index ；
        root.left=build_Tree(inorder,inbegin,index-1,postorder,postbegin,postbegin+index-inbegin-1);
        
        root.right=build_Tree(inorder,index+1,inend,postorder,postbegin+index-inbegin,postend-1);
        
        return root;
        
    }
}