Check if All the Integers in a Range Are Covered
<p>You are given a 2D integer array <code>ranges</code> and two integers <code>left</code> and <code>right</code>. Each <code>ranges[i] = [start<sub>i</sub>, end<sub>i</sub>]</code> represents an <strong>inclusive</strong> interval between <code>start<sub>i</sub></code> and <code>end<sub>i</sub></code>.</p>

<p>Return <code>true</code> <em>if each integer in the inclusive range</em> <code>[left, right]</code> <em>is covered by <strong>at least one</strong> interval in</em> <code>ranges</code>. Return <code>false</code> <em>otherwise</em>.</p>

<p>An integer <code>x</code> is covered by an interval <code>ranges[i] = [start<sub>i</sub>, end<sub>i</sub>]</code> if <code>start<sub>i</sub> &lt;= x &lt;= end<sub>i</sub></code>.</p>

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

<pre>
<strong>Input:</strong> ranges = [[1,2],[3,4],[5,6]], left = 2, right = 5
<strong>Output:</strong> true
<strong>Explanation:</strong> Every integer between 2 and 5 is covered:
- 2 is covered by the first range.
- 3 and 4 are covered by the second range.
- 5 is covered by the third range.
</pre>

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

<pre>
<strong>Input:</strong> ranges = [[1,10],[10,20]], left = 21, right = 21
<strong>Output:</strong> false
<strong>Explanation:</strong> 21 is not covered by any range.
</pre>

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

<ul>
	<li><code>1 &lt;= ranges.length &lt;= 50</code></li>
	<li><code>1 &lt;= start<sub>i</sub> &lt;= end<sub>i</sub> &lt;= 50</code></li>
	<li><code>1 &lt;= left &lt;= right &lt;= 50</code></li>
</ul>
Array; Hash Table; Prefix Sum
func isCovered(ranges [][]int, left int, right int) bool {
	diff := [52]int{}
	for _, e := range ranges {
		l, r := e[0], e[1]
		diff[l]++
		diff[r+1]--
	}
	s := 0
	for i, x := range diff {
		s += x
		if s <= 0 && left <= i && i <= right {
			return false
		}
	}
	return true
}