【剑指Offer 07】重建二叉树

/**
 * 剑指 Offer 07. 重建二叉树
 * https://leetcode.cn/problems/zhong-jian-er-cha-shu-lcof/
 * 思路：前序遍历数组的第一个结点是根结点，在中序遍历数组中找到根结点，根结点左边是是左子树的元素，根结点右边是右子树的元素
 *  递归此过程找出所有子树的根结点
 * */
public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return buildTree(preorder, inorder, 0, 0, preorder.length - 1);
    }

    private TreeNode buildTree(int[] preorder, int[] inorder, int i, int start, int end) {
        if (start > end) {
            return null;
        }
        TreeNode root = new TreeNode(preorder[i]);
        for (int j = start; j <= end; j++) {
            if (inorder[j] == root.val) {
                root.left = buildTree(preorder, inorder, i + 1, start, j - 1);
                root.right = buildTree(preorder, inorder, i + j - start + 1, j + 1, end);
            }
        }
        return root;
    }
}