剑指offer面试题6 重建二叉树（java）

注：（1）java中树的构建

（2）构建子树时可以直接利用Arrays.copyOfRange(preorder, from, to),这个方法是左开右闭的

 package com.xsf.SordForOffer;

 import java.util.Arrays;

 /*剑指offer第6个问题
  根据前序和中序遍历来重建二叉树
  */
 class BinaryTreeNode {
     public int value;
     public BinaryTreeNode leftNode;
     public BinaryTreeNode rightNode;
 }

 class ConstructCore {
     /*
      * 输入二叉树的前序遍历和中序遍历结果,重建二叉树并输出头节点 ex:12473568,47215386
      */
     public BinaryTreeNode constructCore(int[] preorder, int[] inorder)
             throws Exception {

         if (preorder == null || inorder == null) {
             return null;
         }
         if (preorder.length != inorder.length) {
             throw new Exception("长度不一样－非法输入");
         }
         BinaryTreeNode root = new BinaryTreeNode();
         for (int i = 0; i < inorder.length; i++) {
             if (inorder[i] == preorder[0]) {
                 // isHave = true;
                 root.value = inorder[i];
                 root.leftNode = constructCore(
                         Arrays.copyOfRange(preorder, 1, i + 1),
                         Arrays.copyOfRange(inorder, 0, i));
                 root.rightNode = constructCore(
                         Arrays.copyOfRange(preorder, i + 1, preorder.length),
                         Arrays.copyOfRange(inorder, i + 1, inorder.length));
             }
         }

         return root;
     }

     public void lastOrderTraverse(BinaryTreeNode T) {
         if (T != null) {
             lastOrderTraverse(T.leftNode);
             lastOrderTraverse(T.rightNode);
             System.out.print(T.value);
         }
     }
 }

 public class Pro6Biconstruct {
     public static void main(String[] args) throws Exception {
         ConstructCore test = new ConstructCore();
         int[] pre = { 1, 2, 4 };
         int[] in = { 2, 1, 4 };
         BinaryTreeNode root = test.constructCore(pre, in);
         test.lastOrderTraverse(root);
     }
 }