NC_12_reConstructBinaryTree

package org.example.interview.practice;

/**
 * @author xianzhe.ma
 * @date 2021/9/7
 */

public class NC_12_reConstructBinaryTree {

    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        return dfs(0, 0, in.length - 1, pre, in);
    }

    public TreeNode dfs(int preStart, int inStart, int inEnd, int[] preorder, int[] inorder) {
        if (preStart > preorder.length - 1 || inStart > inEnd) {
            return null;
        }
        //创建结点
        TreeNode root = new TreeNode(preorder[preStart]);
        int index = 0;
        //找到当前节点root在中序遍历中的位置，然后再把数组分两半
        for (int i = inStart; i <= inEnd; i++) {
            if (inorder[i] == root.val) {
                index = i;
                break;
            }
        }
        root.left = dfs(preStart + 1, inStart, index - 1, preorder, inorder);
        root.right = dfs(preStart + index - inStart + 1, index + 1, inEnd, preorder, inorder);
        return root;
    }

    public static class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;

        public TreeNode(int val) {
            this.val = val;
        }
    }
}