LeetCode[270] Closest Binary Search Tree Value

LeetCode[270] Closest Binary Search Tree Value

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:
Given target value is a floating point.
You are guaranteed to have only one unique value in the BST that is closest to the target.

Recursion

复杂度
O(N), O(lgN)

思路
用一个变量来记录当前的值，并且在每次recursion之前，比较得到目前的最大值。注意double变量的比较不要用==

代码

double min = Double.MAX_VALUE;
int val = 0;

public int closetValue(TreeNode root, double target) {
    helper(root, target);
    return val;
}

public void helper(TreeNode root, double target) {
    if(root == null) return;
    if(Math.abs(target - root.val) < min) {
        min = Math.abs(target - root.val);
        val = root.val;
    }
    if(root.val > target) {
        helper(root.left, target);
    }
    else {
        helper(root.right, target);
    }
}