《剑指》6

题目：给定一颗二叉树的前序和中序遍历结果，重构该二叉树，并输入其头结点

package offer;public class offer6_ReBuildTree {    /**     * 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，并输出其头结点。     * 假设输入的两种遍历结果中都不含重复的数字     * @param args     */    public static void main(String[] args) {        int[] pre = {1,2,3,4,5,6,7};        int[] in = {3,2,4,1,6,5,7};        TreeNode root = offer6_ReBuildTree.reConstructBinaryTree(pre,in);    }     public static TreeNode reConstructBinaryTree(int [] pre,int [] in) {           if(pre == null || in == null){                return null;            }            TreeNode root = reBuildTree1(pre, 0, pre.length-1, in, 0, in.length-1);            return root;         }        /**         * 第一种         * @param pre         * @param preStart         * @param preEdn         * @param in         * @param inStart         * @param inEdn         * @return         */        public static TreeNode reBuildTree1(int[] pre,int preStart,int preEdn,int[] in,int inStart,int inEdn){            if(inStart > inEdn || preStart>preEdn){                return null;            }            TreeNode node = new TreeNode(pre[preStart]);            preStart++;            while(in[inStart] != node.val && inStart<inEdn){                inStart++;            }            node.left = reBuildTree1(pre, preStart, inStart, in, preStart-1,inStart);            node.right = reBuildTree1(pre, inStart+1, pre.length-1, in, inStart+1, in.length-1);            return node;        }    public static class TreeNode {        int val;        TreeNode left;        TreeNode right;        TreeNode() {        }        TreeNode(int x) {            val = x;        }    }}