Day 23 | 669. Trim a BST | 108. Convert Sorted Array to BST | 538. Convert BST to Greater Tree

LeetCode二叉树问题解决方案集锦,

最新推荐文章于 2025-12-06 07:43:37 发布

原创最新推荐文章于 2025-12-06 07:43:37 发布 · 199 阅读

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LeetCode 669. Trim a Binary Search Tree

Question Link

class Solution {
    public TreeNode trimBST(TreeNode root, int low, int high) {
        if(root == null) return null;
        if(root.val < low)
            return trimBST(root.right, low, high);
        if(root.val > high)
            return trimBST(root.left, low, high);
        // The value of root in the range
        root.left = trimBST(root.left, low, high);
        root.right = trimBST(root.right, low, high);
        return root;
    }
}

LeetCode 108. Convert Sorted Array to Binary Search Tree

Question Link

class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        return traversal(nums, 0, nums.length - 1);
    }

    TreeNode traversal(int[] nums, int low, int high){
        if(low > high)
            return null;
        int middle = low + (high - low)/2;
        TreeNode node = new TreeNode(nums[middle]);
        node.left = traversal(nums, low, middle-1);
        node.right = traversal(nums, middle+1, high);
        return node;
    }
}

low + ((high - low) >> 1) is equals to (low+high)/2. The first one can avoid cross-border problem when high and low are bigest int.

LeetCode 538. Convert BST to Greater Tree

Question Link

class Solution {
    int pre = 0;    // record the value of previous node
    public TreeNode convertBST(TreeNode root) {
        traversal(root);
        return root;
    }

    void traversal(TreeNode root){
        if(root == null)
            return;

        traversal(root.right);
        pre += root.val;
        root.val = pre;
        traversal(root.left);
    }
}