Sync LeetCode submission Runtime - 3 ms (91.54%), Memory - 18.6 MB (12.89%)

Author: jimit105

1028-interval-list-intersections/README.md

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+<p>You are given two lists of closed intervals, <code>firstList</code> and <code>secondList</code>, where <code>firstList[i] = [start<sub>i</sub>, end<sub>i</sub>]</code> and <code>secondList[j] = [start<sub>j</sub>, end<sub>j</sub>]</code>. Each list of intervals is pairwise <strong>disjoint</strong> and in <strong>sorted order</strong>.</p>
+
+<p>Return <em>the intersection of these two interval lists</em>.</p>
+
+<p>A <strong>closed interval</strong> <code>[a, b]</code> (with <code>a &lt;= b</code>) denotes the set of real numbers <code>x</code> with <code>a &lt;= x &lt;= b</code>.</p>
+
+<p>The <strong>intersection</strong> of two closed intervals is a set of real numbers that are either empty or represented as a closed interval. For example, the intersection of <code>[1, 3]</code> and <code>[2, 4]</code> is <code>[2, 3]</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2019/01/30/interval1.png" style="width: 700px; height: 194px;" />
+<pre>
+<strong>Input:</strong> firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24],[25,26]]
+<strong>Output:</strong> [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> firstList = [[1,3],[5,9]], secondList = []
+<strong>Output:</strong> []
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>0 &lt;= firstList.length, secondList.length &lt;= 1000</code></li>
+	<li><code>firstList.length + secondList.length &gt;= 1</code></li>
+	<li><code>0 &lt;= start<sub>i</sub> &lt; end<sub>i</sub> &lt;= 10<sup>9</sup></code></li>
+	<li><code>end<sub>i</sub> &lt; start<sub>i+1</sub></code></li>
+	<li><code>0 &lt;= start<sub>j</sub> &lt; end<sub>j</sub> &lt;= 10<sup>9</sup> </code></li>
+	<li><code>end<sub>j</sub> &lt; start<sub>j+1</sub></code></li>
+</ul>

1028-interval-list-intersections/solution.py

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+# Approach 1: Merge Intervals
+
+# M, N = lengths of `firstList` and `secondList` respectively
+# Time: O(M + N)
+# Space: O(M + N)
+
+class Solution:
+    def intervalIntersection(self, firstList: List[List[int]], secondList: List[List[int]]) -> List[List[int]]:
+        ans = []
+        i = j = 0
+
+        while i < len(firstList) and j < len(secondList):
+            # Let's check if firstList[i] intersects secondList[j].
+            # lo - the startpoint of the intersection
+            # hi - the endpoint of the intersection
+            lo = max(firstList[i][0], secondList[j][0])
+            hi = min(firstList[i][1], secondList[j][1])
+            if lo <= hi:
+                ans.append([lo, hi])
+
+            # Remove the interval with the smallest endpoint
+            if firstList[i][1] < secondList[j][1]:
+                i += 1
+            else:
+                j += 1
+
+        return ans