Lists

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# CSCI-UA 102
## Data Structures

<br>

## Lists (Part 2)

.author[
Instructor: Uday Kusupati <br><br><br>
]

.license[
Copyright 2020 Joanna Klukowska. Unless noted otherwise all content is released under  a <br>
[Creative Commons Attribution-ShareAlike 4.0 International License](https://creativecommons.org/licenses/by-sa/4.0/)]

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.bottom-left[© Joanna Klukowska. CC-BY-SA.]

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## Add to list. Putting it all together?

Try to come up with a single Java method that implements
the `add` method from our interface:

```Java
// adds an element 'it' at position pos, shifts elements starting at pos by
// one position to the right (higher position values)
// throws NoSuchElementException if pos < 0 or pos >= size
public boolean add(E it, int pos) throws NoSuchElementException;
```

You will need to use all of the code fragments from the previous slides, plus a bit
more to locate the position.

Assume that there is a `size` data field that keeps track of the exact number of
elements in the list.

Make sure that your function works when the list is empty, when it has only one element,
and when it has many elements.

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### Group Discussion: Putting it all together?

With your group, try to come up with a single Java method that implements
the `add` method from our interface:

Assume that there is a `size` data field that keeps track of the exact number of
elements in the list.

Make sure that your function works when the list is empty, when it has only one element,
and when it has many elements.

-->
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## Searching in a Linked List

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## Searching in a Linked List

- To find an element in an unsorted array, we need to iterate through the array.

- The search in a linked list is similar and we will use the ideas of iterating through the list
with just a slight modification.

.left-column2[
Code for iterating through the list:

```
Node current = head;
while (current != null ) {
    current = current.next;
}
```
{{content}}
]

Let's say we are implementing the `find()` method from our interface:

```
// determines if 'it' is in the list
// and if so returns its position,
// otherwise returns -1
public int find (E it) ;
```

--
name: find-implementation

What would this method look like?

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template: find-implementation

```java
public int find (E it) {

//what should be initialized
    //and checked

Node<E> current = head;

//does the condition need to change
    while (current != null ) {

current = current.next;
        // anything else here?
    }

//decide what to return

}
```

---
template: find-implementation

```java
public int find (E it) {

//start the counter
    int counter = 0;

Node<E> current = head;

//does the condition need to change
    while (current != null ) {

current = current.next;
        counter++;  //we just passed a node
    }

//decide what to return

}
```

---
template: find-implementation

```java
public int find (E it) {

//start the counter
    int counter = 0;

Node<E> current = head;

//stop if we reach the end or find it
    while (current != null
            && !current.data.equals(it)) {
        current = current.next;
        counter++;  //we just passed a node
    }

//decide what to return

}
```

---
template: find-implementation
name: find-final

```java
public int find (E it) {

//start the counter
    int counter = 0;

Node<E> current = head;

//stop if we reach the end or find it
    while (current != null
            && !cureent.data.euals(it)) {
        current = current.next;
        counter++;  //we just passed a node
    }
    //if the list is empty,
    //or we went to the end
    if (current == null)
        return -1;
    return counter;
}
```

---
template: find-final

.left-column2[
<div style="transform:translateY(-5em);">
.red[
- __What happens when `it == null`?__
- __What happens if we allow elements stored in the nodes to be `null`?__
]
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]

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