Second Freebie!!! This one is marked as "easy"
This problem was asked by Google.
Given two singly linked lists that intersect at some point, find the intersecting node. The lists are non-cyclical.
For example, given A = 3 -> 7 -> 8 -> 10 and B = 99 -> 1 -> 8 -> 10, return the node with value 8.
In this example, assume nodes with the same value are the exact same node objects.
Do this in O(M + N) time (where M and N are the lengths of the lists) and constant space.
C solution
I got it with one integer and two pointers.
#include <stdlib.h>
typedef struct node {
struct node * next;
int val; } node;
node * list_intersection(node * head_a, node * head_b) {
int diff = 0;
node * this_a = head_a, * this_b = head_b;
while(this_a != NULL) {
this_a = this_a->next;
diff++; }
while(this_b != NULL) {
this_b = this_b->next;
diff--; }
this_a = head_a;
this_b = head_b;
while(this_a != this_b) {
if(diff >= 0) {
this_a = this_a->next;
diff--; }
if(diff < 0) {
this_b = this_b->next;
diff++; }}
return this_a; }
