/** 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。*/
public class Main7 {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 reConstructBinaryTree = reConstructBinaryTree(pre, in);}public static TreeNode reConstructBinaryTree(int [] pre,int [] in) {TreeNode root = reConstructBinaryTree(pre, 0, pre.length-1, in, 0, in.length-1);return root;}public static TreeNode reConstructBinaryTree(int [] pre, int preStart, int preEnd, int [] in, int inStart, int inEnd) {if(preStart>preEnd||inStart>inEnd){return null;}//新建一个TreeNodeTreeNode root = new TreeNode(pre[preStart]);//对中序数组进行输入边界的遍历for(int i=inStart; i<=inEnd; i++){if(in[i]==pre[preStart]){//重构左子树，注意边界条件root.left = reConstructBinaryTree(pre, preStart+1, preStart+i-inStart, in, inStart, i-1);//重构右子树，注意边界条件root.right = reConstructBinaryTree(pre, i-inStart+preStart+1, preEnd, in, i+1, inEnd);}}return root;}
}
class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int x) { val = x; }}