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109.java
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109.java
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__________________________________________________________________________________________________
sample 0 ms submission
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
static ListNode h;
public TreeNode sortedListToBST(ListNode head) {
if (head == null) return null;
h = head;
int len = getLength(h);
return getList(0, len-1);
}
public int getLength(ListNode h) {
int len = 0;
ListNode p =h;
while (p!= null) {
p = p.next;
len++;
}
return len;
}
public TreeNode getList(int start, int end) {
if (start > end) return null;
int mid = (start + end)/2;
TreeNode left = getList(start, mid-1);
TreeNode root = new TreeNode(h.val);
h = h.next;
TreeNode right = getList(mid+1,end);
root.left = left;
root.right = right;
return root;
}
}
__________________________________________________________________________________________________
sample 36944 kb submission
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
//Date:019-02-20
//Start: 13:09
//End: 14:00. Runtime: 3 ms, faster than 11.54%; Memory Usage: 37.8 MB, less than 98.19%.
public TreeNode sortedListToBST(ListNode head){
if (head == null) {
return null;
}
ListNode mid = findMiddle(head).get(1);
TreeNode res = new TreeNode(mid.val);
if (head.next == null) {
return res;
}
helper2(res, head);
return res;
}
public void insert(TreeNode node, int value) {
if (node == null) {
return;
}
//很重要,避免插入重复值
if (value == node.val) {
return;
}
int rootVal;
while (true) {
rootVal = node.val;
if (value < rootVal) {
if (node.left == null) {
node.left = new TreeNode(value);
break;
} else {
node = node.left;
}
} else {
if (node.right == null) {
node.right = new TreeNode(value);
break;
} else {
node = node.right;
}
}
}
}
public List<ListNode> findMiddle(ListNode node) {
ListNode slow = node;
ListNode preSlow = slow;
ListNode fast = node;
while (fast != null && fast.next != null) {
preSlow = slow;
slow = slow.next;
fast = fast.next.next;
}
List<ListNode> res = new ArrayList<ListNode>();
res.add(preSlow);
res.add(slow);
return res;
}
public void helper2(TreeNode root, ListNode node) {
if (node == null) {
return;
}
ListNode mid = findMiddle(node).get(1);
ListNode preMid = findMiddle(node).get(0);
insert(root, mid.val);
if (node.next == null) {
return;
}
ListNode right = mid.next;
preMid.next = null;
ListNode left = node;
helper2(root, left);
helper2(root, right);
}
}
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