剑指offer面试题6 重建二叉树（java）

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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

 1 package com.xsf.SordForOffer; 2  3 import java.util.Arrays; 4  5 /*剑指offer第6个问题 6  根据前序和中序遍历来重建二叉树 7  */ 8 class BinaryTreeNode { 9     public int value;10     public BinaryTreeNode leftNode;11     public BinaryTreeNode rightNode;12 }13 14 class ConstructCore {15     /*16      * 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:12473568,4721538617      */18     public BinaryTreeNode constructCore(int[] preorder, int[] inorder)19             throws Exception {20         21         if (preorder == null || inorder == null) {22             return null;23         }24         if (preorder.length != inorder.length) {25             throw new Exception("长度不一样－非法输入");26         }27         BinaryTreeNode root = new BinaryTreeNode();28         for (int i = 0; i < inorder.length; i++) {29             if (inorder[i] == preorder[0]) {30                 // isHave = true;31                 root.value = inorder[i];32                 root.leftNode = constructCore(33                         Arrays.copyOfRange(preorder, 1, i + 1),34                         Arrays.copyOfRange(inorder, 0, i));35                 root.rightNode = constructCore(36                         Arrays.copyOfRange(preorder, i + 1, preorder.length),37                         Arrays.copyOfRange(inorder, i + 1, inorder.length));38             }39         }40         41         return root;42     }43 44     public void lastOrderTraverse(BinaryTreeNode T) {45         if (T != null) {46             lastOrderTraverse(T.leftNode);47             lastOrderTraverse(T.rightNode);48             System.out.print(T.value);49         }50     }51 }52 53 public class Pro6Biconstruct {54     public static void main(String[] args) throws Exception {55         ConstructCore test = new ConstructCore();56         int[] pre = { 1, 2, 4 };57         int[] in = { 2, 1, 4 };58         BinaryTreeNode root = test.constructCore(pre, in);59         test.lastOrderTraverse(root);60     }61 }

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