Contains Duplicate II

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

思路：用set记录每个数字，对于距离超过k的从set中擦出。

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        int n = nums.size();
        set<int> check;
        for (int i = 0; i < n; i++)
        {
            if (i > k) check.erase(nums[i - k - 1]);
            if (check.count(nums[i])) return true;
            check.insert(nums[i]);
        }
        return false;
    }
};