number-of-intersecting-interval-pairs-i

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Algorithms

You are given a 2D integer array <code>intervals</code> of <code>n</code> elements, where <code>intervals[i] = [starti, endi]</code> represents the closed interval from <code>starti</code> to <code>endi</code>.

Return the number of pairs of indices <code>(i, j)</code> such that <code>0 &lt;= i &lt; j &lt; n</code> and <code>intervals[i]</code> and <code>intervals[j]</code> intersect.

Two intervals intersect if they have at least one point in common, including when they only share an endpoint.

&nbsp;
Example 1:

<div class="example-block">
Input: intervals = [[1,2],[2,3],[3,4]]

Output: 2

Explanation:

There are 2 intersecting interval pairs:

<ul>
	<li>Intervals <code>[1, 2]</code> and <code>[2, 3]</code> intersect at the point 2.</li>
	<li>Intervals <code>[2, 3]</code> and <code>[3, 4]</code> intersect at the point 3.</li>
</ul>
</div>

Example 2:

<div class="example-block">
Input: intervals = [[1,5],[2,4],[3,6]]

Output: 3

Explanation:

There are 3 intersecting interval pairs:

<ul>
	<li>The intersection of <code>[1, 5]</code> and <code>[2, 4]</code> is <code>[2, 4]</code>.</li>
	<li>The intersection of <code>[1, 5]</code> and <code>[3, 6]</code> is <code>[3, 5]</code>.</li>
	<li>The intersection of <code>[2, 4]</code> and <code>[3, 6]</code> is <code>[3, 4]</code>.</li>
</ul>
</div>

Example 3:

<div class="example-block">
Input: intervals = [[1,2],[3,4],[5,6]]

Output: 0

Explanation:

There are no intersecting interval pairs. Hence, the answer is 0.
</div>

&nbsp;
Constraints:

<ul>
	<li><code>2 &lt;= n == intervals.length &lt;= 100</code></li>
	<li><code>intervals[i] = [starti, endi]</code></li>
	<li><code>0 &lt;= starti &lt;= endi &lt;= 100</code></li>
</ul>