Java各种数据结构实现

1、单向链表

实现思路：创建Node类，包括自己的数据和指向下一个；创建Node类，包括头尾节点，实现添加、删除、输出等功能。

tips：n = n.next不破坏链表结果，而n.next = n.next.next就等于是n节点的next属性变成了再下一个，即指向n+1个节点的指针丢失，但实际上n+1节点仍在，只不过从链表中去除。

具体代码：

public class NodeList<Integer> {
    class Node<Integer> {
        Node<Integer> next = null; //指向下一节点
        Integer data; //节点所存数据

        //Node类构造方法
        public Node(Integer d) {
            this.data = d;
        }
    }
    Node<Integer> head; //链表的头节点
    Node<Integer> last; //链表的尾节点
    int length; //链表长度

    //链表的无参构造方法
    public NodeList() {
        this.head = new Node<Integer>(null); //头节点为空
    }

    //创建链表的同时添加第一个数据
    public NodeList(Integer d) {
        this.head = new Node<Integer>(d);
        this.last = head; //此时头尾节点一样
        length++;
    }

    //尾部添加节点
    public void add(Integer d) {
        if (head == null) {
            head = new Node<Integer>(d);
            last = head;
            length++;
        } else {
            Node<Integer> newNode = new Node<Integer>(d);
            last.next = newNode; //令之前的尾节点指向新节点
            last = newNode; //新节点成为尾节点
            length++;
        }
    }

    //删除指定数据
    public boolean del(Integer d) {
        if (head == null) {
            return false;
        }
        Node<Integer> n = head; //从头开始判断
        if (n.data == d) {
            head = head.next;
            length--;
            return true;
        } 

        while (n.next != null) {
            if (n.next.data == d) {
                n.next = n.next.next; //n节点指向了n+2节点
                length--;
                return true;
            }
            n = n.next; //正常移动不破坏链表
        }
        return false;
    }
    public void print() {
        if (head == null) {
            System.out.println("此链表为空！");
        }
        Node<Integer> n = head;
        while (n != null) {
            System.out.println(n.data+",");
            n = n.next;
        }
    }
}

2016-12-13 16:22:13

2、栈（链式结构）

实现思路：仍然使用节点，最重要的是栈顶节点top，利用其完成压、弹栈操作。

tips：出栈就是改栈顶为下一个，压栈就是新栈顶与原栈顶建立链接。

具体代码：

public class Stack {
    class Node {
        Object data;
        Node next = null;

        public Node(Object d) {
            this.data = d;
        }
    }

    Node top; //创建栈顶节点

    //出栈
    public Object pop() {
        if (top != null) {
            Object d = top.data;
            top = top.next; //栈顶改为下一个
            return d;
        }
        return null;
    }

    //压栈
    public void push(Object d) {
        Node n = new Node(d);
        n.next = top; //与原栈进行连接
        top = n;
    }

    //输出栈顶的元素
    public Object peek() {
        return top.data;
    }
}

2016-12-14 14:14:12

3、队列（链式结构）

实现思路：创建首尾节点first、last，实现入队出队操作。

tips：记得判断是否为空。

具体代码：

public class Queue {
    class Node {
        Object data;
        Node next;

        public Node(Object d) {
            this.data = d;
        }
    }

    //创建队首队尾指针
    Node first;
    Node last;

    //入队
    public void enQueue(Object d) {
        if (first == null) {
            first = new Node(d);
            last = first;
        } else {
            last.next = new Node(d); //原队尾指向新节点
            last = last.next; //更改队尾
        }
    }

    //出队
    public Object deQueue() {
        if (first != null) {
            Object item = first.data; //保存原队首数据
            first = first.next; //更改队首
            return item;
        }
        return null;
    }
}

2016-12-14 14:27:16

4、树的遍历

4.1、前序preorder

顺序：根左右

非递归：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Preorder in ArrayList which contains node values.
     */
    public List<Integer> preorderTraversal(TreeNode root) {
        Stack<TreeNode> stack = new Stack<TreeNode>();
        List<Integer> preorder = new ArrayList<Integer>();
        if (root == null) {
            return preorder;
        }
        stack.push(root);
        while (!stack.empty()) {
            TreeNode node = stack.pop();
            preorder.add(node.val);
            if (node.right != null) {
                stack.push(node.right);
            }
            if (node.left != null) {
                stack.push(node.left);
            }
        }
        return preorder;
    }
}

Traverse：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Preorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> preorderTraversal(TreeNode root) {
        ArrayList<Integer> preorder = new ArrayList<Integer>();
        helper(root, preorder);
        return preorder;
    }
    private void helper(TreeNode root, ArrayList<Integer> preorder) {
        if (root == null) {
            return;
        }
        preorder.add(root.val);
        helper(root.left, preorder);
        helper(root.right, preorder);
    }

Divide & Conquer：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Preorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> preorderTraversal(TreeNode root) {
        ArrayList<Integer> preorder = new ArrayList<Integer>();
        if (root == null) {
            return preorder;
        }
        //Divide
        ArrayList<Integer> left = preorderTraversal(root.left);
        ArrayList<Integer> right = preorderTraversal(root.right);
        //Conquer
        preorder.add(root.val);
        preorder.addAll(left);
        preorder.addAll(right);
        return preorder;
    }
}

4.2、中序inorder

顺序：左根右

非递归：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        Stack<TreeNode> stack = new Stack<TreeNode>();
        ArrayList<Integer> inorder = new ArrayList<Integer>();
        TreeNode curt = root;
        while (curt != null || !stack.empty()) {
            while (curt != null) {
                stack.add(curt);
                curt = curt.left;
            }
            curt = stack.peek();
            stack.pop();
            inorder.add(curt.val);
            curt = curt.right;
        }
        return inorder;
    }
}

Traverse：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        ArrayList<Integer> inorder = new ArrayList<Integer>();
        helper(root, inorder);
        return inorder;
    }
    private void helper(TreeNode root, ArrayList<Integer> inorder) {
        if (root == null) {
            return;
        }
        helper(root.left, inorder);
        inorder.add(root.val);
        helper(root.right, inorder);
    }
}

Divide & Conquer：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        ArrayList<Integer> inorder = new ArrayList<Integer>();
        if (root == null) {
            return inorder;
        }
        ArrayList<Integer> left = inorderTraversal(root.left);
        ArrayList<Integer> right = inorderTraversal(root.right);
        inorder.addAll(left);
        inorder.add(root.val);
        inorder.addAll(right);
        return inorder;
    }
}

4.3、后序postorder

顺序：左右根

非递归：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Postorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> postorderTraversal(TreeNode root) {
        ArrayList<Integer> postorder = new ArrayList<Integer>();
        Stack<TreeNode> stack = new Stack<TreeNode>();
        TreeNode prev = null; //前一个遍历节点
        TreeNode curr = root;
        if (root == null) {
            return postorder;
        }
        stack.push(root);
        while (!stack.empty()) {
            curr = stack.peek();
            if (prev == null || prev.left == curr || prev.right == curr) {
                //往下遍历
                if (curr.left != null) {
                    stack.push(curr.left);
                } else if (curr.right != null) {
                    stack.push(curr.right);
                }
            } else if (curr.left == prev) {
                //从左往上遍历
                if (curr.right != null) {
                    stack.push(curr.right);
                }
            } else {
                //从右往上遍历
                postorder.add(curr.val);
                stack.pop();
            }
            prev = curr;
        }
        return postorder;
    }
}

递归与上面一样

2017-01-27