<p>Given an integer array <code>nums</code> and an integer <code>k</code>, return <code>true</code> <em>if there are two <strong>distinct indices</strong> </em><code>i</code><em> and </em><code>j</code><em> in the array such that </em><code>nums[i] == nums[j]</code><em> and </em><code>abs(i - j) &lt;= k</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3,1], k = 3
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,0,1,1], k = 1
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3,1,2,3], k = 2
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-10<sup>9</sup> &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
	<li><code>0 &lt;= k &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        constexpr int HashBits = 10;
        constexpr int HashSize = 1 << HashBits;
        constexpr int HashMask = (1 << HashBits) - 1;
        array<int, HashSize> table;
        table.fill(-(k+1));
        for (int i = 0; i < nums.size(); ++i) {
            int x = nums[i];
            int h = hash(x) & HashMask;
            if ((i - table[h]) <= k) {
                if (nums[table[h]] == x) return true;
                for (int j = max(0, i - k); j < table[h]; ++j) {
                    if (nums[i] == nums[j])
                        return true;
                }
            }
            table[h] = i;
        }
        return false;
    }
private:
    inline int hash(int x) {
    	x = ((x >> 16) ^ x) * 0x45d9f3bU;
	    x = ((x >> 16) ^ x) * 0x45d9f3bU;
	    x = (x >> 16) ^ x;
	    return x;
        // x ^= x >> 11;
        // x ^= x >> 13;
        // return x;
    }
};
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