LeetCode 219 Contains Duplicate II

Problem:

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 difference between i and j is at most k.

Summary:

给出数组nums，整型数k，找到数组中是否存在nums[i]和nums[j]相等且i - j小于k的情况。

Solution:

开始用最简单写法，两重for循环逐一查找，出现TLE。

后用HashMap改进，key为数组中出现的数字，value为最近出现位置的下标。

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