https://leetcode.com/problems/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

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

程式碼：

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

　　unordered_map<int, int> mp 查詢 值 x 存在：① mp.find(x) != mp.end(); ② mp.count(x) != 0;

自己寫了一個 $O(n^2)$ 的程式碼 不出所料的掛掉了 然後查了一下 unordered_map 的用法 $O(logn)$ 的時間還是很快的 比我寫的那個不知道快到哪裡去了  但是一個 Easy 題被我搞成這樣也太涼了吧