使用排序數組/鏈表構建二叉搜尋樹

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2018-08-13 11:29:05

一、Convert Sorted Array to Binary Search Tree

問題描述：

問題求解：

    public TreeNode sortedArrayToBST2(int[] nums) {        if (nums == null || nums.length == 0) {            return null;        }        return helper(0, nums.length - 1, nums);    }    private TreeNode helper (int start, int end, int[] nums) {        if (start > end) {            return null;        }        int mid= start + (end - start) / 2;        TreeNode root = new TreeNode(nums[mid]);        root.left = helper(start, mid - 1, nums);        root.right = helper(mid + 1, end , nums);        return root;    }

二、Convert Sorted List to Binary Search Tree

問題描述：

問題求解：

    public TreeNode sortedListToBST(ListNode head) {        if (head == null) return null;        return helper(head, null);    }    private TreeNode helper(ListNode head, ListNode tail) {        if (head == tail) return null;        ListNode mid = getMid(head, tail);        TreeNode root = new TreeNode(mid.val);        root.left = helper(head, mid);        root.right = helper(mid.next, tail);        return root;    }    private ListNode getMid(ListNode head, ListNode tail) {        ListNode slow = head;        ListNode fast = head;        while (fast != tail && fast.next != tail) {            slow = slow.next;            fast = fast.next.next;        }        return slow;    }

 

使用排序數組/鏈表構建二叉搜尋樹