Contains Duplicate II

Desicription

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:

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

Example 2:

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

Example 3:

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

Solution

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class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_map<int, vector<int>> book;
        for(int i = 0; i < nums.size(); i++) {
            if(book.find(nums[i]) == book.end()) {
                book[nums[i]] = vector<int>();
            }
            book[nums[i]].push_back(i);
        }
        for(const auto& num : book) {
            for(int i = 1; i < num.second.size(); i++) {
                if(num.second[i] - num.second[i - 1] <= k) {
                    return true;
                }
            }
        }
        return false;
    }
};