Contains Duplicate III](https://leetcode.com/problems/contains-duplicate-iii/)(Medium)

Given an array of integers, find out whether there are two distinct indices i and j in the array such that the difference between nums[i] and nums[j] is at most t and the difference between i and j is at most k.

题目大意：

给定一个整数数组，判断其中是否存在两个不同的下标i和j满足：| nums[i] - nums[j] | <= t 并且 | i - j | <= k

解题思路： 维护一个大小为 k的二叉搜索树，来一个新的元素时，在BST上二分搜索有没有符合条件的数对，动态更新这个BST。因为BST的大小为 k 或不超过 k，所以这里面的数下标的差值一定是符合条件的。

TreeMap is implemented as a red black tree, which is a self-balancing binary search tree.

public boolean containsNearbyAlmostDuplicate(int[] nums, int k, int t) {
    if (k < 1 || t < 0)
        return false;

    TreeSet<Integer> set = new TreeSet<Integer>();

    for (int i = 0; i < nums.length; i++) {
        int c = nums[i];
        if ((set.floor(c) != null && c <= set.floor(c) + t)
                || (set.ceiling(c) != null && c >= set.ceiling(c) -t))
            return true;

        set.add(c);

        if (i >= k)
            set.remove(nums[i - k]);
    }

    return false;
}