leetcode219. 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 is at most k.

Example 1:

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Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

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Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

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Input: nums = [1,2,3,1,2,3], k = 2
Output: false

适用无序关联式容器，unordered_map<int,int>，key是数字，value是坐标的映射，如果哈希表中存在这个数字，并且当前数字的索引减去这个数字的索引小于等于k，就返回真，否则将这个数字的索引存入哈希表中。

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bool (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;
        m[nums[i]]=i;
    }
    return false;
}