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) {
        // write code here
        if(preOrder.length == 0){
            return null;
        }

        int rootVal = preOrder[0];
        TreeNode result = new TreeNode(rootVal);
        int index = findRootIndex(inOrder,rootVal);
        TreeNode left = buildTreeII(Arrays.copyOfRange(preOrder,1,index+1),Arrays.copyOfRange(inOrder,0,index));
        TreeNode right = buildTreeII(Arrays.copyOfRange(preOrder,index+1,preOrder.length),Arrays.copyOfRange(inOrder,index+1,inOrder.length));
        result.left = left;
        result.right = right;
        return result;
    }

    public int findRootIndex(int[] arr,int rootVal){
        for(int i = 0;i < arr.length;i++){
            if(arr[i] == rootVal){
                return i;
            }
        }
        return -1;
    }
}