LeetCode Contains Duplicate II

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

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_map<int, int> last;
        
        int len = nums.size();
        for (int i=0; i<len; i++) {
            int val = nums[i];
            auto iter = last.find(val);
            if (iter == last.end()) {
                last.insert(make_pair(val, i));
                continue;
            }
            if (i - iter->second <= k) {
                return true;
            }
            iter->second = i;
        }
        return false;
    }
};

 第二轮反而写的更挫了：

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