add solution for #986 Interval List Intersections.

problems/interval-list-intersections/README.md

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+# Interval List Intersections
+
+LeetCode #: [986](https://leetcode.com/problems/interval-list-intersections/)
+
+Difficulty: Medium
+
+Topics: Two Pointers.
+
+## Problem
+
+Given two lists of closed intervals, each list of intervals is pairwise disjoint and in sorted order.
+
+Return the intersection of these two interval lists.
+
+(Formally, 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 is either empty, or can be represented as a closed interval.  For example, the intersection of [1, 3] and [2, 4] is [2, 3].)
+
+Example 1:
+
+```text
+Input: A = [[0,2],[5,10],[13,23],[24,25]], B = [[1,5],[8,12],[15,24],[25,26]]
+Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]
+Reminder: The inputs and the desired output are lists of Interval objects, and not arrays or lists.
+```
+
+Note:
+
+- `0 <= A.length < 1000`
+- `0 <= B.length < 1000`
+- `0 <= A[i].start, A[i].end, B[i].start, B[i].end < 10^9`
+
+NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.
+
+## Complexity Analysis
+
+Assume m is the length of array A and n is the length of array B.
+
+Time complexity: O(m+n)
+
+Space complexity: O(1) (excluding the result output array)

problems/interval-list-intersections/intervalIntersection.js

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+/**
+ * @param {number[][]} A
+ * @param {number[][]} B
+ * @return {number[][]}
+ */
+const intervalIntersection = function (A, B) {
+  const result = []
+  let i = 0
+  let j = 0
+
+  while (i < A.length && j < B.length) {
+    const lo = Math.max(A[i][0], B[j][0])
+    const hi = Math.min(A[i][1], B[j][1])
+
+    if (lo <= hi) {
+      result.push([lo, hi])
+    }
+
+    if (A[i][1] < B[j][1]) {
+      i++
+    } else {
+      j++
+    }
+  }
+
+  return result
+}
+
+module.exports = intervalIntersection

problems/interval-list-intersections/intervalIntersection.test.js

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+const intervalIntersection = require('./intervalIntersection')
+
+test('Example 1', () => {
+  const A = [[0, 2], [5, 10], [13, 23], [24, 25]]
+  const B = [[1, 5], [8, 12], [15, 24], [25, 26]]
+
+  const result = intervalIntersection(A, B)
+
+  expect(result).toStrictEqual([
+    [1, 2], [5, 5], [8, 10], [15, 23], [24, 24], [25, 25]
+  ])
+})