L11 Search Range in Binary Search Tree
Given two values k1 and k2 (where k1 < k2) and a root pointer to a Binary Search Tree. Find all the keys of tree in range k1 to k2. i.e. print all x such that k1<=x<=k2 and x is a key of given BST. Return all the keys in ascending order.
Example
If k1 =10
and k2 =22
, then your function should return[12, 20, 22]
.
20
/ \
8 22
/ \
4 12
感觉structure跟之前拿到判断是否合法BST有点像。
public ArrayList<Integer> searchRange(TreeNode root, int k1, int k2) {
ArrayList<Integer> res = new ArrayList<>();
if (root == null) {
return res;
}
helper(root, k1, k2, res);
return res;
}
private void helper(TreeNode root, int k1, int k2, ArrayList<Integer> res) {
if (root == null) {
return;
}
if (root.val > k1) {
helper(root.left, k1, k2, res);
}
if (root.val >= k1 && root.val <= k2) {
res.add(root.val);
}
if (root.val < k2) {
helper(root.right, k1, k2, res);
}
}
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