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leetcode--Convert Sorted Array to Binary Search Tree

2024-07-07 07:19:03   223人阅读

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

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/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] num) {
        return transferHelper(num, 0, num.length);
    }
     
    /**construct tree node with the help of indices.<br>
     * @param num --input array
     * @param i --left index which is included.
     * @param j --right index which is excluded
     * @return root node of the tree
     */
    private TreeNode transferHelper(int[] num, int i, int j){
        TreeNode root = null;
        if(j > i){
            if(j == i + 1)
                root = new TreeNode(num[i]);
            else{
                int mid = i + (j - i) / 2;
                root = new TreeNode(num[mid]);
                root.left = transferHelper(num, i, mid);
                root.right = transferHelper(num, mid + 1, j);
            }
        }
        return root;
    }
}

　　


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