LC.P108[将有序数组转换为二叉搜索树]

方法一：DFS

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/**
 * 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 build(nums, 0, nums.length - 1);
    }

    private TreeNode build(int[] nums, int left, int right) {
        if (left > right) return null;
        int mid = left + right >> 1;
        TreeNode node = new TreeNode(nums[mid]);
        node.left = build(nums, left, mid - 1);
        node.right = build(nums, mid + 1, right);
        return node;
    }
}
  • 时间复杂度：$O(n)$
  • 空间复杂度：$O(logn)$