根據前序遍歷和後序遍歷重建二叉樹

前序遍歷與後序遍歷 重建二叉樹的關鍵在於如何寫好遞歸代碼段中幾個節點。

具體代碼如下所示

public class TreeNode {

        public int data;
        TreeNode leftNode;
        TreeNode rightNode;
        public TreeNode(int data){
            this.data = data;
        }
    public  static TreeNode rebuildBinaryTree(int[] preorder,int[] inorder){
        if(preorder==null||inorder==null){
            return null;
        }
        TreeNode root=rebuildBinaryTreeCore(preorder,0,preorder.length-1,inorder,0,inorder.length-1);
        return root;
    }
    public static TreeNode rebuildBinaryTreeCore(int[] preorder,int startpreorder,int endpreorder,int[] inorder,int startinorder,int endinorder){
        if(startpreorder>endpreorder||startinorder>endinorder){
            return null;
        }
        TreeNode root=new TreeNode(preorder[startpreorder]);
        for(int i=startinorder;i<=endinorder;i++){
            if(preorder[startpreorder]==inorder[i]){
                root.leftNode = rebuildBinaryTreeCore(preorder,startpreorder+1,startpreorder+i-startinorder,inorder,startinorder,i-1);
                root.rightNode = rebuildBinaryTreeCore(preorder,i-startinorder+startpreorder+1,endpreorder,inorder,i+1,endinorder);
            }
        }
        return root;
    }
    public static void printpostorder(TreeNode root){
        if(root ==null){
            return;
        }else{
            printpostorder(root.leftNode);
            printpostorder(root.rightNode);
            System.out.println(root.data);
        }

    }

    public static void main(String[] args) {
        int[] preorder = {3,9,20,15,7};
        int[] inorder =  {9,3,15,20,7};

        TreeNode node = rebuildBinaryTree(preorder,inorder);
        printpostorder(node);

    }
}