[LeetCode] Contains Duplicate II

Well, the basic idea is fairly straightforward. We maintain a mapping

mp

from a value in

nums

to its position (index)

i

. Each time we meet an unseen value, we add it to the map (

mp[nums[i]] = i

). Otherwise, depending on whether the recorded index

mp[nums[i]]

and the current index

i

satisfy

i - mp[nums[i]] <= k

(node that the new index

i

is larger than the old index

mp[nums[i]]

), we return

true

or update the index (

mp[nums[i]] = i

). If all the elements have been visited and we have not returned

true

, we will return

false

.

bool containsNearbyDuplicate(vector<int>& nums, int k) {
unordered_map<int, int> mp;
for (int i = 0; i < nums.size(); i++) {
if (mp.find(nums[i]) != mp.end() && i - mp[nums[i]] <= k)
return true;
mp[nums[i]] = i;
}
return false;
}