p108

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LeetCode p108 Convert Sorted Array to Binary Search Tree 题解

1.题目：

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

题意：

输入一个数组将它转换为二叉平衡查找树。

2.解题思路:

dp取中间~一步步将树拓展开来。

3.代码

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/**
 * 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) {
       if (nums.length < 1)
			return null;
		if (nums.length == 1) {
			return new TreeNode(nums[0]);
		}
		int len = nums.length;
		TreeNode tNode = new TreeNode(nums[len / 2]);
		dp(nums, 0, len / 2 - 1, tNode, true);
		dp(nums, len / 2 + 1, len - 1, tNode, false);
		return tNode;
	}

	public void dp(int[] nums, int left, int right, TreeNode tNode,
			boolean l) {

		if (left > right)
			return;
		int mid = (right - left) / 2 + left;
		TreeNode t = new TreeNode(nums[mid]);
		if (l) {
			System.out.println("left" + t.val);
			tNode.left = t;
		} else {
			System.out.println("right" + t.val);
			tNode.right = t;
		}
		dp(nums, left, mid - 1, t, true);
		dp(nums, mid + 1, right, t, false);

	}
}

4.一些总结：