标签：binary target treeset nim tco example diff rsa int
原题链接在这里：https://leetcode.com/problems/minimum-absolute-difference-in-bst/#/description
题目：
Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.
Example:
Input:
1
3
/
2
Output:
1
Explanation:
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).
Note: There are at least two nodes in this BST.
题解：
Binary Tree Inorder Traversal, 由于是BST, 所以是asending的, 取出最小difference.
Time Complexity: O(n). Space: O(logn), stack space.
AC Java:
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 int min = Integer.MAX_VALUE; 12 Integer pre = null; 13 public int getMinimumDifference(TreeNode root) { 14 if(root == null){ 15 return min; 16 } 17 getMinimumDifference(root.left); 18 19 if(pre != null){ 20 min = Math.min(min, root.val-pre); 21 } 22 pre = root.val; 23 24 getMinimumDifference(root.right); 25 return min; 26 } 27 }
如果不是BST的话可以借助于TreeSet<Integer> ts, 对于每一个node, 找出node.val在ts中的floor和ceil, 计算minimum difference. 再把node 本身的val加到ts中.
Time Complexity: O(nlogn). Space: O(n), ts size.
AC Java:
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 int min = Integer.MAX_VALUE; 12 TreeSet<Integer> ts = new TreeSet<Integer>(); 13 14 public int getMinimumDifference(TreeNode root) { 15 if(root == null){ 16 return min; 17 } 18 19 if(!ts.isEmpty()){ 20 if(ts.floor(root.val) != null){ 21 min = Math.min(min, root.val-ts.floor(root.val)); 22 } 23 if(ts.ceiling(root.val) != null){ 24 min = Math.min(min, ts.ceiling(root.val)-root.val); 25 } 26 } 27 ts.add(root.val); 28 29 getMinimumDifference(root.left); 30 getMinimumDifference(root.right); 31 return min; 32 } 33 }
LeetCode Minimum Absolute Difference in BST
标签：binary target treeset nim tco example diff rsa int
原文地址：http://www.cnblogs.com/Dylan-Java-NYC/p/6676394.html
