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Java实现思路

public class SingleLinkList<E> {
    // 元素数量
    private int size;
    // 头节点
    private Node<E> first;
    static final int ELEMENT_NOT_FOUND = -1;

    private static class Node<E> {
        E element;
        Node<E> next;

        public Node(E element, Node<E> next) {
            this.element = element;
            this.next = next;
        }
    }

    /**
     * 清空
     */
    public void clear() {
        first = null;
        size = 0;
    }

    /**
     * 是否为空
     */
    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return size;
    }

    /**
     * get
     * @param index
     * @return
     */
    public E get(int index) {
        return node(index).element;
    }

    /**
     * set 返回旧值
     * @param index
     * @param element
     */
    public E set(int index, E element) {
        Node<E> node = node(index);
        E oldElement = node.element;
        node.element = element;
        return oldElement;
    }

    /**
     * 尾部添加
     * @param index
     * @param element
     */
    public void add(int index, E element) {
        rangeCheckForAdd(index);
        if (index == 0) {
            first = new Node<E>(element, first);
        } else {
            Node<E> pre = node(index-1);
            pre.next = new Node<E>(element, pre.next);
        }
        size++;
    }

    /**
     * 指定索引删除
     */
    public E remove(int index) {
        rangeCheck(index);
        Node<E> node = first;
        if (index == 0) {
            first = first.next;
        } else {
            Node<E> pre = node(index-1);
            node = pre.next;
            pre.next = node.next;
         }
        size --;
        return node.element;
    }

    /**
     * 元素返回索引值
     */
    public int indexOf(E element) {
        if (element == null) {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (node.element == null) return i;
                node = node.next;
            }
        } else {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (element.equals(node.element)) return i;
                node = node.next;
            }
        }
        return ELEMENT_NOT_FOUND;
    }

    /***
     * 获取index位置的节点对象
     */
    private Node<E> node(int index) {
        rangeCheck(index);

        Node<E> node = first;
        for (int i = 0; i < index; i++) {
            node = node.next;
        }
        return node;
    }

    /**
     * 检查索引
     */
    private void rangeCheck(int index) {
        if (index < 0 || index >= size) {
            outOfBounds(index);
        }
    }

    private void outOfBounds(int index) {
        throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
    }

    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > size) {
            outOfBounds(index);
        }
    }

    @Override
    public String toString() {

        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(",[");
        Node<E> node = first;
        for (int i = 0; i < size; i++) {
            if (i != 0) string.append(",");
            string.append(node.element);
            node = node.next;
        }
        string.append("]");
        return string.toString();
    }
}

Swift

import Foundation

class Node<E> {
    var element: E
    var next: Node?
    init(element: E, next: Node?) {
        self.element = element
        self.next = next
    }
}

struct SingleLinkList<E: Comparable> {
    // 元素数量
    private var size: Int?
    // 头节点
    private var first: Node<E>?

    let ELEMENT_NOT_FOUND: Int = -1
    
    var isEmpty: Bool {
        return first == nil
    }
    
    /**
     get
     */
    public func get(index: Int) -> E {
        return node(index: index).element
    }
    
    /**
     set
     */
    public func set(index: Int, newElement: E) -> E {
        let currNode = node(index: index)
        let oldElement: E = currNode.element
        currNode.element = newElement
        return oldElement
    }
    /**
     清空
     */
    mutating public func clear() {
        first = nil
        size = 0
    }
    /**
     尾部添加元素
     */
    mutating public func add(index: Int, newElement: E) {
        rangCheckForAdd(index: index)
        if index == 0 {
            first = Node(element: newElement, next: first)
        } else {
            let pre = node(index: index-1)
            pre.next = Node(element: newElement, next: pre.next)
        }
        size = (size ?? 0) + 1
    }
    /**
     按索引删除
     */
    mutating public func remove(index: Int) -> E {
        rangCheck(index: index)
        let currNode = first!
        if index == 0 {
            first = currNode.next
        } else {
            let preNode = node(index: index-1)
            let tempNode = preNode.next
            preNode.next = tempNode!.next
        }
        size = size! - 1
        return currNode.element
    }
    /**
     按元素返回索引值
     */
    public func indexOf(element: E) -> Int {
        var curNode = first;
        var i = 0
        while i < size! {
            if curNode?.element == element {
                return i
            }
            curNode = curNode?.next
            i = i + 1
        }
        return ELEMENT_NOT_FOUND
    }
    /**
     获取index位置的节点对象
     */
    private func node(index: Int) -> Node<E> {
        rangCheck(index: index)
        var node = first;
        var i: Int = 0
        while i < index {
            node = node?.next
            i = i + 1
        }
        return node!
    }
    
    private func rangCheck(index: Int) {
        if index < 0 || index >= size! {
            outOfBounds(index: index)
        }
    }
    
    private func rangCheckForAdd(index: Int) {
        if index < 0 || index > size ?? 0 {
            outOfBounds(index: index)
        }
    }
    
    private func outOfBounds(index: Int) {
        print("Index: \(index) , Size = \(String(describing: size))")
    }    
}