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669. 修剪二叉搜索树

题目链接: 修剪二叉搜索树

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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 trimBST(TreeNode root, int low, int high) {
        if(root == null) {
            return null;
        }
        if(root.val < low) {
            TreeNode right = trimBST(root.right,low,high);
            return right;
        }
        if(root.val > high) {
            TreeNode left = trimBST(root.left,low,high);
            return left;
        }
        root.left = trimBST(root.left,low,high);
        root.right = trimBST(root.right,low,high);
        return root;
    }
}

108.将有序数组转换为二叉搜索树

题目链接: 将有序数组转换为二叉搜索树

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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 traversal(nums,0,nums.length - 1);
    }
    public TreeNode traversal(int[] nums,int left,int right) {
        if(left > right) {
            return null;
        }

        TreeNode root = new TreeNode();
        int middle = left + (right - left) / 2;
        root.val = nums[middle];

        root.left = traversal(nums,left,middle - 1);
        root.right = traversal(nums,middle + 1,right);

        return root;
    }
}

538.把二叉搜索树转换为累加树

题目链接: 把二叉搜索树转换为累加树

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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 {
    int pre;
    public TreeNode convertBST(TreeNode root) {
        pre = 0;
        traversal(root);
        return root;
    }

    public void traversal(TreeNode root) {
        if(root == null) {
            return;
        }
        traversal(root.right);
        root.val += pre;
        pre = root.val;
        traversal(root.left);
    }
}