160. Intersection of Two Linked Lists (axross#115)

Author: Kohei Asai

solutions/intersectionOfTwoLinkedLists.test.ts

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+import {
+  createSinglyLinkedListNode,
+  getNthNode
+} from "../testUtilities/LinkedList";
+import { SinglyLinkedListNode } from "../types/LinkedList";
+import getIntersectionNode from "./intersectionOfTwoLinkedLists";
+
+describe("160. Intersection of Two Linked Lists", () => {
+  const TEST_CASES: [any, number[], number[], number, number][] = [
+    [8, [4, 1, 8, 4, 5], [5, 0, 1, 8, 4, 5], 2, 3],
+    [2, [0, 9, 1, 2, 4], [3, 2, 4], 3, 1],
+    [0, [2, 6, 4], [1, 5], 3, 2]
+  ];
+
+  for (const [, valuesA, valuesB, skipA, skipB] of TEST_CASES) {
+    const headA = createSinglyLinkedListNode(valuesA);
+    const headB = createSinglyLinkedListNode(valuesB);
+    let intersection: SinglyLinkedListNode<number> | null = null;
+
+    if (skipA < valuesA.length) {
+      intersection = getNthNode(headA!, skipA);
+
+      getNthNode(headB!, skipB - 1).next = intersection;
+    }
+
+    it(`returns the ${skipA}th node of "linked list A" when called with [${valuesA}], [${valuesB}], ${skipA} and ${skipB}`, () => {
+      expect(getIntersectionNode(headA, headB)).toBe(intersection);
+    });
+  }
+});

solutions/intersectionOfTwoLinkedLists.ts

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+import { SinglyLinkedListNode } from "../types/LinkedList";
+
+// 160. Intersection of Two Linked Lists
+// https://leetcode.com/problems/intersection-of-two-linked-lists/
+export default function getIntersectionNode<T>(
+  headA: SinglyLinkedListNode<T> | null,
+  headB: SinglyLinkedListNode<T> | null
+): SinglyLinkedListNode<T> | null {
+  let a = headA;
+  let b = headB;
+
+  while (a !== b) {
+    a = a ? a.next : headB;
+    b = b ? b.next : headA;
+  }
+
+  return a;
+}