1.描述

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.

2.分析

用集合s存放最大距離為k之間的數(shù)組元素，依次遍歷數(shù)組。
放入規(guī)則：遍歷數(shù)組元素為nums[i]，在集合s中查找nums[i]是否在集合中，如果在，則返回true。
取出規(guī)則：遍歷數(shù)組元素為nums[i]，如果i>k, 則從集合中取出nums[i-k-1]。

3.代碼

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        if (k <= 0) return false;
        if (k > nums.size()) k = nums.size() - 1;
        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;
    }
};