# LeetCode's Linked List

Merge sorted linked list, Add two numbers, Swap nodes in pairs

### 1. Merge two sorted linked lists and return it as a new list.

Example:

```
- Input: 1 -> 3-> 5 & 2 -> 4-> 6
Output: 1 -> 2-> 3 -> 4 -> 5 -> 6
```

Approach:

```
- Traverse both list at the same time, compare their values at each step and
add the smaller one to a new list.
```

Cost:

```
- O(n|m) time, O(n+m) space where n and m are lengths of these two linked lists.
```

### 2. Given two linked lists representing two non-negative number, add them together and return it as a linked list.

Assumption:

```
- The digits are stored in reverse order.
- Each node contains a single digit.
```

Example:

```
- Input: (1 -> 6 -> 4) + (2 -> 4-> 1)
Output: (3 -> 0 -> 6)
```

Approach:

```
- Traverse both lists and keep track of the sum and carry for each
digit.
```

Cost:

```
- O(n|m) time, O(m|n) space where m and m are lengths of these two lists.
```

### 3. Given a linked list, swap every two adjacent nodes and return its head.

Assumption:

```
- If the length of the linked list is odd, the last node should not be swapped.
- The solution should use constant space.
```

Example:

```
- Input: 1 -> 3-> 5 -> 2 -> 4-> 6
Output: 3 -> 1-> 2 -> 5 -> 6 -> 4
- Input: 1 -> 3-> 5 -> 2 -> 4
Output: 3 -> 1-> 2 -> 5 -> 4
```

Approach:

```
- Traverse the list and swap the nodes pairwise by adjusting where it's pointing next.
```

Cost:

```
- O(n) time, O(1) space where n is the length of a linked list.
```

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Tagged: #leetcode, #algorithm