二叉树的中序遍历是升序序列,数组有序,可以确保是中序遍历,但中序遍历无法完全确定一棵二叉树。即结果不唯一。
每次以数组的中间数字作为二叉树的“根”结点,左右子树的元素分别位于“根”结点的两遍,依次递归结束
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public TreeNode sortedArrayToBST(int[] nums) {
return helper(nums,0,nums.length-1);
}
public TreeNode helper(int[] nums,int left,int right){
if(left>right){
return null;
}
int mid=(left+right)/2;
TreeNode root=new TreeNode(nums[mid]);
root.left=helper(nums,left,mid-1);
root.right=helper(nums,mid+1,right);
return root;
}
}
原文:https://www.cnblogs.com/zhimeng-yabiao/p/14609084.html