leetcode 108 Convert Sorted Array to Binary Search Tree ----- java

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Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

 

給一個排好序的數組，然後求搜尋二叉樹

其實就是二分法，不難。

 

 

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public TreeNode sortedArrayToBST(int[] nums) {        int len = nums.length;        if( len == 0)            return null;        return helper(nums,0,(len-1)/2,len-1);    }    public TreeNode helper(int[] nums,int start,int mid,int end){                if( start > end )            return null;        TreeNode node = new TreeNode(nums[mid]);        node.left = helper(nums,start,(mid+start-1)/2,mid-1);        node.right = helper(nums,mid+1,(end+mid+1)/2,end);        return node;    }}

 

leetcode 108 Convert Sorted Array to Binary Search Tree ----- java