【剑指offer】重建二叉树

题目描述

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

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public class TestReConstructBinaryTree {    public TreeNode reConstructBinaryTree(int[] pre, int[] in) {        TreeNode root = reConstructBinaryTree(pre, 0, pre.length - 1, in, 0, in.length - 1);        return root;    }    // 前序遍历{1,2,4,7,3,5,6,8} 中序遍历序列{4,7,2,1,5,3,8,6}    public TreeNode reConstructBinaryTree(int[] pre, int preStart, int preEnd, int[] in, int inStart, int inEnd) {        if (preStart > preEnd || inStart > inEnd) {            return null;        }        TreeNode root = new TestReConstructBinaryTree().new TreeNode(pre[preStart]);// 根节点        for (int i = inStart; i <= inEnd; i++) {// 遍历中序列            if (in[i] == pre[preStart]) {                int leftLength = i - inStart;// 左子树长度                root.left = reConstructBinaryTree(pre, preStart + 1, preStart + leftLength, in, inStart, i - 1);                root.right = reConstructBinaryTree(pre, preStart + leftLength + 1, preEnd, in, i + 1, inEnd);            }        }        return root;    }    // 递归前序遍历    public void preOrder(TreeNode t) {        if (t != null) {            System.out.print(t.val);            preOrder(t.left);            preOrder(t.right);        }    }    //树节点定义    class TreeNode {        int val;        TreeNode left;        TreeNode right;        TreeNode() {        }        TreeNode(int x) {            val = x;        }    }    public static void main(String[] args) {        int[] pre = {1,2,4,7,3,5,6,8};        int[] in = {4,7,2,1,5,3,8,6};        TreeNode t = new TestReConstructBinaryTree().reConstructBinaryTree(pre, in);        new TestReConstructBinaryTree().preOrder(t) ;    }}