dnshi
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diff --git a/‎algorithms/IntervalListIntersections.js
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 |1008|[Construct Binary Search Tree from Preorder Traversal](https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal)|[JavaScript](algorithms/ConstructBinarySearchTreeFromPreorderTraversal.js)|Medium|
 |1002|[Find Common Characters](https://leetcode.com/problems/find-common-characters)|[JavaScript](algorit
10000
hms/FindCommonCharacters.js)|Easy|
 |989|[Add to Array-Form of Integer](https://leetcode.com/problems/add-to-array-form-of-integer)|[JavaScript](algorithms/AddToArrayFormOfInteger.js)|Easy|
+|986|[Interval List Intersections](https://leetcode.com/problems/interval-list-intersections)|[JavaScript](algorithms/IntervalListIntersections.js)|Medium|
 |977|[Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array)|[JavaScript](algorithms/SquaresOfASortedArray.js)|Easy|
 |965|[Univalued Binary Tree](https://leetcode.com/problems/univalued-binary-tree)|[JavaScript](algorithms/UnivaluedBinaryTree.js)|Easy|
 |961|[N-Repeated Element in Size 2N Array](https://leetcode.com/problems/n-repeated-element-in-size-2n-array)|[JavaScript](algorithms/N-RepeatedElementInSize2NArray.js)|Easy|
 
@@ -0,0 +1,71 @@
+// Source : https://leetcode.com/problems/interval-list-intersections
+// Author : Dean Shi
+// Date   : 2022-01-07
+
+/***************************************************************************************
+ * You are given two lists of closed intervals, firstList and secondList, where
+ * firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each list of
+ * intervals is pairwise disjoint and in sorted order.
+ * 
+ * Return the intersection of these two interval lists.
+ * 
+ * A closed interval [a, b] (with a <= b) denotes the set of real numbers x with a <= x
+ * <= b.
+ * 
+ * The intersection 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 [1, 3]
+ * and [2, 4] is [2, 3].
+ * 
+ * Example 1:
+ * 
+ * Input: firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24]
+ * ,[25,26]]
+ * Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]
+ * 
+ * Example 2:
+ * 
+ * Input: firstList = [[1,3],[5,9]], secondList = []
+ * Output: []
+ * 
+ * Constraints:
+ * 
+ * 0 <= firstList.length, secondList.length <= 1000
+ * firstList.length + secondList.length >= 1
+ * 0 <= starti < endi <= 109
+ * endi < starti+1
+ * 0 <= startj < endj <= 109
+ * endj < startj+1
+ * 
+ * 
+ ***************************************************************************************/
+
+/**
+ * @param {number[][]} firstList
+ * @param {number[][]} secondList
+ * @return {number[][]}
+ */
+var intervalIntersection = function(firstList, secondList) {
+    const result = []
+    let firstPt = 0
+    let secondPt = 0
+    let firstItem = firstList[firstPt]
+    let secondItem = secondList[secondPt]
+    while (firstItem && secondItem) {
+        let openingPoint = Math.max(firstItem[0], secondItem[0])
+        let closedPoint = Math.min(firstItem[1], secondItem[1])
+
+        if (closedPoint >= openingPoint) {
+            result.push([openingPoint, closedPoint])
+        }
+
+        if (firstItem[1] > secondItem[1]) {
+            secondItem = secondList[++secondPt]
+        } else if (firstItem[1] < secondItem[1]) {
+            firstItem = firstList[++firstPt]
+        } else {
+            firstItem = firstList[++firstPt]
+            secondItem = secondList[++secondPt]
+        }
+    }
+    return result
+};