LeetCode[219] 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 difference between i and j is at most k.

建立哈希表，值为下标，顺序遍历nuns元素，若发现相等元素，计算 i - hash[nums[i]]，若满足则返回true。若大于k，更新hash[nums[i]]，因为 i 的值只会越来越大，先前的下标值已经没有意义了。

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