Leetcode theme [array] -219- duplicate Element II exists

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Their thinking ：

1. First, analyze the meaning of the topic by combining the topic stem , Given an array nums And a number k, Whether there is a subscript i,j So that two different subscripts do not differ by more than k I want to wait
2. According to the meaning extracted above , You can turn the problem into , At a length of K+1(i-j<=k, Then count i In itself , The maximum length of the sliding window is k+1) To find out if there are two identical numbers , This is the time , The problem-solving model has been established
3. There is an upper limit of the window , Then you need to discard the elements when you reach the upper limit , At this time, the leftmost element of the window is discarded , Subscript to be i-k-1(i-k For the first element in the sliding window , What needs to be discarded needs to be subtracted again )
4. Last question , How to mark that an element has already appeared ？ When solving array problems , We often use hash table to store tag bits

func containsNearbyDuplicate(nums []int, k int) bool {
    numsToFlag := map[int]bool{}
    for i := 0; i < len(nums); i++ {
        if i > k {
            numsToFlag[nums[i-k-1]] = false
        }
        if numsToFlag[nums[i]] {
            return true
        }
        numsToFlag[nums[i]] = true
    }
    return false
}