剑指offer--重建二叉树

/*
 * 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TreeNode
        TreeNode 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; }
 }