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First, traverse both linked lists to determine their lengths. Calculate the difference in lengths and advance the pointer of the longer list by the length difference. Then move both pointers in tandem to find the intersection node.
Time Complexity: O(m + n).
Space Complexity: O(1).
1#include <stdio.h>
2#include <stdlib.h>
3
4struct ListNode {
5 int val;
6 struct ListNode *next;
7};
8
9int getLength(struct ListNode *head) {
10 int length = 0;
11 while (head) {
12 length++;
13 head = head->next;
14 }
15 return length;
16}
17
18struct ListNode *getIntersectionNode(struct ListNode *headA, struct ListNode *headB) {
19 int lenA = getLength(headA);
20 int lenB = getLength(headB);
21
22 if (lenA > lenB) {
23 for (int i = 0; i < lenA - lenB; i++)
24 headA = headA->next;
25 } else {
26 for (int i = 0; i < lenB - lenA; i++)
27 headB = headB->next;
28 }
29
30 while (headA != headB) {
31 headA = headA->next;
32 headB = headB->next;
33 }
34 return headA;
35}This solution first determines the lengths of both lists. It advances the pointer for the longer list by the difference in lengths. Then, it compares nodes in both lists step by step to find the intersection.
Use two pointers, each starting at the head of one list. Traverse the list until a pointer reaches null, then start traversing the other list from the beginning. Repeat until the two pointers meet at the intersection node.
Time Complexity: O(m + n).
Space Complexity: O(1).
1class
The Python solution follows the two pointer method where each pointer traverses its list, and when reaching the end, starts from the beginning of the other list. This continues until they meet at an intersection node or at the end as null.