remove_duplicates.go

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func deleteDuplicates(head *ListNode) *ListNode {
    // check head isn't nil (null)
    if head == nil {
        return nil
    }
    
    // two pointers head, and next node. algorithm is drop next node if it's equal to the first ptr's value.
    for ptr1, ptr2 := head, head.Next; ptr2 != nil; ptr2 = ptr2.Next {
        // equal
        if (ptr1.Val == ptr2.Val) {
            // drop next value
            ptr1.Next = ptr2.Next
            // set second pointer to be traversed to new next node
            ptr2 = ptr1
        } else {
            // traverse ptr1, since it's sorted if the next node is different, there are no more similar nodes.
            ptr1 = ptr1.Next
        }
    }
    // pointer to head
    return head
    
}