根据前序遍历和中序遍历创建出二叉树

二叉树

class Solution {
    public static void main(String[] args) {

    }

    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if (preorder == null || preorder.length == 0) {
            return null;
        }
        int begin = 0;
        int start = 0;
        int end = preorder.length - 1;
        return buildTree2(preorder, inorder, begin, start, end);

    }

    public TreeNode buildTree2(int[] preorder, int[] inorder, int begin, int start, int end) {
        if (start > end) {
            return null;
        }
        int root = preorder[begin];
        TreeNode node = new TreeNode(root);
        int k = search(inorder, start, end, root);
        node.left = buildTree2(preorder, inorder, begin + 1, start, k - 1);
        node.right = buildTree2(preorder, inorder, begin + k - start + 1, k + 1, end);
        return node;

    }

    public int search(int[] inorder, int start, int end, int obj) {
        for (int i = start; i <= end; ++i) {
            if (obj == inorder[i]) {
                return i;
            }
        }
        return 0;
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }

}