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package leetcode;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Stack;
/**
* Project Name : Leetcode
* Package Name : leetcode
* File Name : ClosestBinarySearchTreeValueII
* Creator : Edward
* Date : Dec, 2017
* Description : 272. Closest Binary Search Tree Value II
*/
public class ClosestBinarySearchTreeValueII {
/**
* Given a non-empty binary search tree and a target value, find k values in the BST that are closest to the target.
Note:
Given target value is a floating point.
You may assume k is always valid, that is: k ≤ total nodes.
You are guaranteed to have only one unique set of k values in the BST that are closest to the target.
8
/ \
3 9
/ \
2 7
target : 6 k = 2
Stack : pred : 3
Stack : succ : 9
3 1
res : 7 8
* @param root
* @param target
* @param k
* @return
*/
// time : O(n) space : O(n)
public List<Integer> closestKValues(TreeNode root, double target, int k) {
LinkedList<Integer> res = new LinkedList<>();
helper(res, root, target, k);
return res;
}
private void helper(LinkedList<Integer> res, TreeNode root, double target, int k) {
if (root == null) return;
helper(res, root.left, target, k);
if (res.size() == k) {
if (Math.abs(target - root.val) < Math.abs(target - res.peekFirst())) {
res.removeFirst();
} else return;
}
res.add(root.val);
helper(res, root.right, target, k);
}
// time : O(klogn)
public List<Integer> closestKValues2(TreeNode root, double target, int k) {
List<Integer> res = new ArrayList<>();
Stack<TreeNode> pred = new Stack<>();
Stack<TreeNode> succ = new Stack<>();
iniPred(root, target, pred);
iniSucc(root, target, succ);
if (!pred.isEmpty() && !succ.isEmpty() && succ.peek().val == pred.peek().val) {
helper(pred, false);
}
while (k-- > 0) {
if (succ.isEmpty()) {
res.add(helper(pred, false));
} else if (pred.isEmpty()) {
res.add(helper(succ, true));
} else {
double succDiff = Math.abs((double)succ.peek().val - target);
double predDiff = Math.abs((double)pred.peek().val - target);
if (succDiff < predDiff) {
res.add(helper(succ, true));
} else {
res.add(helper(pred, false));
}
}
}
return res;
}
private void iniSucc(TreeNode root, double target, Stack<TreeNode> succ) {
while (root != null) {
if (root.val == target) {
succ.push(root);
break;
} else if (root.val > target) {
succ.push(root);
root = root.left;
} else {
root = root.right;
}
}
}
private void iniPred(TreeNode root, double target, Stack<TreeNode> pred) {
while (root != null) {
if (root.val == target) {
pred.push(root);
break;
} else if (root.val < target) {
pred.push(root);
root = root.right;
} else {
root = root.left;
}
}
}
private int helper(Stack<TreeNode> stack, boolean isSucc) {
TreeNode cur = stack.pop();
int res = cur.val;
if (isSucc) cur = cur.right;
else cur = cur.left;
while (cur != null) {
stack.push(cur);
if (isSucc) cur = cur.left;
else cur = cur.right;
}
return res;
}
}