219. 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 absolute difference between i and j is at most k.

Example 1:

Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2
Output: false
// Hash map
bool containsNearbyDuplicate(vector<int>& nums, int k) { // time: O(n); space: O(n)
    unordered_map<int, int> mp;
    for (int i = 0; i < nums.size(); ++i) {
        if (mp.count(nums[i]) && i - mp[nums[i]] <= k) {
            return true;
        }
        mp[nums[i]] = i;
    }
    return false;
}
// Hash set
bool containsNearbyDuplicate(vector<int>& nums, int k) { // time: O(n); space: O(n)
    unordered_set<int> st;
    for (int i = 0; i < nums.size(); ++i) {
        if (i > k) {
            st.erase(nums[i - k - 1]);
        }
        if (st.count(nums[i])) return true;
        st.insert(nums[i]);
    }
    return false;
}

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