题解 | #牛群的树形结构重建II#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param preOrder int整型一维数组
     * @param inOrder int整型一维数组
     * @return TreeNode类
     */
    public TreeNode buildTreeII (int[] preOrder, int[] inOrder) {
        if (inOrder.length == 0 && preOrder.length == 0) {
            return null;
        }
        int headv = preOrder[0];
        TreeNode head = new TreeNode(headv);
        int count = 0;
        for (int i = 0; i < inOrder.length; i++) {
            if (inOrder[i] == headv) {
                break;
            }
            count++;
        }
        int[] inleft = Arrays.copyOfRange(inOrder, 0, count);
        int[] inright = Arrays.copyOfRange(inOrder, count + 1, inOrder.length);
        int[] poleft = Arrays.copyOfRange(preOrder, 1, count + 1);
        int[] poright = Arrays.copyOfRange(preOrder, count + 1, inOrder.length);
        TreeNode left = buildTreeII(poleft, inleft);
        TreeNode right = buildTreeII(poright, inright);
        head.left = left;
        head.right = right;
        return head;
    }
}