LeetCode 219 Contains Duplicate II

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Contains Duplicate II - LeetCode

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

---

暴力

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) 
    {
        unordered_map<int, pair<int, int>> m;
        for (int i = 0; i < nums.size(); i ++ ) {
            int num = nums[i];
            if (!m[num].first) m[num].first = i + 1;
            else if (!m[num].second) m[num].second = i + 1;
            else if ((i - m[num].second) < (m[num].second - m[num].first)) {
                m[num].first = m[num].second, m[num].second = i + 1;
            }
        }
        for (auto it : m) {
            pair<int, int> p = it.second;
            if (p.second && p.second - p.first <= k) return true;
        }
        return false;
    }
};

set维护一个长度为k的区间

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