LeetCode No.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.

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题目链接：https://leetcode.com/problems/contains-duplicate-ii/

题目大意：给定一个数组，求数组中是否存在j - i <= k使得nums[i] = nums[j]

思路：使用set记录前k个数值，每增加一个都需要将下标i - k - 1对应的数值从set中删掉。

参考代码：

class Solution {public:    bool containsNearbyDuplicate(vector<int>& nums, int k) {        int n = nums.size() ;        if ( n == 0 || k <= 0 )            return false ;        set <int> s ;        for ( int i = 0 ; i < n ; i ++ )        {            if ( i - k - 1 >= 0 )                s.erase ( nums[i-k-1] ) ;            if ( s.find ( nums[i] ) != s.end() )                return true ;            s.insert ( nums[i] ) ;        }        return false ;    }};