二叉树篇

BST树

 

 

递归直接实现。

/*** 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 dfs(nums,0,nums.length-1);}private TreeNode dfs(int [] nums,int left,int right){if(left>right){return null;}//以升序数组的中间元素作为根节点rootint mid=(left+right)/2;TreeNode root = new TreeNode(nums[mid]);//构建root的左子树与右子树root.left=dfs(nums,left,mid-1);root.right=dfs(nums,mid+1,right);return root;}
}