Maximum Frequency of an Element After Performing Operations I
<p>You are given an integer array <code>nums</code> and two integers <code>k</code> and <code>numOperations</code>.</p>

<p>You must perform an <strong>operation</strong> <code>numOperations</code> times on <code>nums</code>, where in each operation you:</p>

<ul>
	<li>Select an index <code>i</code> that was <strong>not</strong> selected in any previous operations.</li>
	<li>Add an integer in the range <code>[-k, k]</code> to <code>nums[i]</code>.</li>
</ul>

<p>Return the <strong>maximum</strong> possible <span data-keyword="frequency-array">frequency</span> of any element in <code>nums</code> after performing the <strong>operations</strong>.</p>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [1,4,5], k = 1, numOperations = 2</span></p>

<p><strong>Output:</strong> <span class="example-io">2</span></p>

<p><strong>Explanation:</strong></p>

<p>We can achieve a maximum frequency of two by:</p>

<ul>
	<li>Adding 0 to <code>nums[1]</code>. <code>nums</code> becomes <code>[1, 4, 5]</code>.</li>
	<li>Adding -1 to <code>nums[2]</code>. <code>nums</code> becomes <code>[1, 4, 4]</code>.</li>
</ul>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [5,11,20,20], k = 5, numOperations = 1</span></p>

<p><strong>Output:</strong> <span class="example-io">2</span></p>

<p><strong>Explanation:</strong></p>

<p>We can achieve a maximum frequency of two by:</p>

<ul>
	<li>Adding 0 to <code>nums[1]</code>.</li>
</ul>
</div>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= k &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= numOperations &lt;= nums.length</code></li>
</ul>
Array; Binary Search; Prefix Sum; Sorting; Sliding Window
func maxFrequency(nums []int, k int, numOperations int) (ans int) {
	cnt := make(map[int]int)
	d := make(map[int]int)
	for _, x := range nums {
		cnt[x]++
		d[x] = d[x]
		d[x-k]++
		d[x+k+1]--
	}

	s := 0
	keys := make([]int, 0, len(d))
	for key := range d {
		keys = append(keys, key)
	}
	sort.Ints(keys)
	for _, x := range keys {
		s += d[x]
		ans = max(ans, min(s, cnt[x]+numOperations))
	}

	return
}
