# Remove Duplicates from Sorted List II Problem

## Description

LeetCode Problem 82.

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

Example 1:

``````1
2
Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]
``````

Example 2:

``````1
2
Input: head = [1,1,1,2,3]
Output: [2,3]
``````

Constraints:

• The number of nodes in the list is in the range [0, 300].
• -100 <= Node.val <= 100
• The list is guaranteed to be sorted in ascending order.

## Sample C++ Code

``````1
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class Solution {
public:
ListNode* deleteDuplicates(ListNode* head) {
if ((head == NULL) || (head->next == NULL))

ListNode* curr = head;
map<int, int> cnt;
while (curr != NULL) {
if (cnt.find(curr->val) != cnt.end()) {
cnt[curr->val] ++;
} else {
cnt[curr->val] = 1;
}
curr = curr->next;
}

int first_num;
bool is_empty = true;
for (map<int,int>::iterator mit = cnt.begin(); mit != cnt.end();
mit ++) {
if (mit->second == 1) {
first_num = mit->first;
is_empty = false;
break;
}
}
if (is_empty)
return NULL;

ListNode* prev;
while (curr != NULL) {
if (curr->val == first_num) {
break;
}
curr = curr->next;
}

while (curr != NULL) {
if (cnt[curr->val] == 1) {
prev->next = curr;
prev = prev->next;
}
curr = curr->next;
}
prev->next = NULL;
}
};
``````