q160_intersection_of_two_linked_lists

//https://leetcode.com/problems/intersection-of-two-linked-lists/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
if (headA == null || headB == null) {
	return null;
}
ListNode a = headA, b = headB;
while(a != null) {
	if(b == null) {
		b = headB;
		a = a.next;
} else if (a == b) {
	return a;
} else {
	b = b.next;
}
}
return null;
    }
}

1 2 3 4 5 -> null

2 3 4 5 


import java.util.*;
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
	HashSet<ListNode> set = new HashSet<>();
	ListNode a = headA;
	while(a != null){
		set.add(a);
		a = a.next;
	}
	while(b != null){
		if(set.contains(b)){
			return b;
}
b = b.next;
}
	return null;
    }
}



// JW
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
	ListNode a = headA, b = headB;	

	while(a != null || b != null){	
		if(a == null) a = headB;
		else if(b == null) b = headA;
		else if(a == b) return a;
		else{
			a = a.next;
			b = b.next;
		}
	}	
	return null;
    }
}
// YW
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
	 if(headA == null || headB == null) return null;
	ListNode a = headA, b = headB;

	while(a != b) {
		
		if(a == null && b == null) {
return null;
} else if(a == null) {
a = headB
} else if(b == null) {
b = headA
} else { 
a = a.next;
b = b.next;
}


		// b null? -> b-> 

		// a, b
	
}
	
return a
    }
}
// JE
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
	ListNode a = headA, b = headB;
	while(a != null || b != null){
		if(a == b) {
			return a;
} else if (a == null){
	a = headB;
} else if (b == null){
	b = headA;
} else {
	a = a.next;
	b = b.next;
}
}
return null;
    }
}