递归

class Solution { // 1. 确定函数参数以及返回值 public TreeNode trimBST(TreeNode root, int low, int high) { // 2.确定终止条件 if (root == null) return null; // 3. 确定单层递归逻辑 // 返回下一层合适的节点 if (root.val < low) return trimBST(root.right, low, high); if (root.val > high) return trimBST(root.left, low, high); // 上一层连接下一层合适节点 root.left = trimBST(root.left, low, high); root.right = trimBST(root.right, low, high); return root; } }

迭代

class Solution { public TreeNode trimBST(TreeNode root, int low, int high) { if (root == null) return null; // 处理头节点将root移动到[L,R]范围内 while (root.val < low || root.val > high) { if (root.val < low) root = root.right;// 小于L向右走 else root = root.left; // 大于R向左走 } TreeNode cur = root; // 此时root已经在[L,R]范围内，处理左孩子小于L的情况 while (cur != null) { while (cur.left != null && cur.left.val < low) { cur.left = cur.left.right; } cur = cur.left; } // 处理右孩子大于R的情况 cur = root; while (cur != null) { while (cur.right != null && cur.right.val > high) { cur.right = cur.right.left; } cur = cur.right; } return root; } }