经典算法面试题整理

冒泡法

package com.gzl.test;

public class bubble {

public static void main(String[] args) {
// TODO Auto-generated method stub
int[] arr={5,2,3,18,6,4,0};
bubble b=new bubble();
b.bubblem(arr);
}
public int[] bubblem(int[] a){
int arr[]=a;
for(int i=0;i<arr.length-1;i++){
for(int j=0;j<arr.length-1-i;j++){
if(arr[j]>arr[j+1]){
int temp=arr[j];
arr[j]=arr[j+1];
arr[j+1]=temp;
}
}
}
for(int i=0;i<arr.length;i++){
System.out.print("..."+arr[i]);
}
return arr;
}
}


选择法
package com.gzl.test;

public class choose {

public static void main(String[] args) {
// TODO Auto-generated method stub
int[] arr={5,2,3,18,6,4,0};
for(int i=0;i<arr.length;i++){
int min=i;
for(int j=i+1;j<arr.length;j++){
if(arr[min]>arr[j]){
int temp=arr[min];
arr[min]=arr[j];
arr[j]=temp;
}
}
}
for(int i=0;i<arr.length;i++){
System.out.print("..."+arr[i]);
}
}

}

递归求n阶乘

public int nonrecursion(int n){
int result=1;
for(int i=1;i<=n;i++){
result=result*i;
}
return result;
}

单链表
public class LinkList {
public Node head;
public Node current;

//方法：向链表中添加数据
public void add(int data) {
//判断链表为空的时候
if (head == null) {//如果头结点为空，说明这个链表还没有创建，那就把新的结点赋给头结点
head = new Node(data);
current = head;
} else {
//创建新的结点，放在当前节点的后面（把新的结点合链表进行关联）
current.next = new Node(data);
//把链表的当前索引向后移动一位
current = current.next;
}
}

//方法重载：向链表中添加结点
public void add(Node node) {
if (node == null) {
return;
}

if (head == null) {
head = node;
current = head;
} else {
current.next = node;
current = current.next;
}
}

//方法：遍历链表（打印输出链表。方法的参数表示从节点node开始进行遍历
public void print(Node node) {
if (node == null) {
return;
}

current = node;
while (current != null) {
System.out.println(current.data);
current = current.next;
}
}

//方法：检测单链表是否有环
public boolean hasCycle(Node head) {

if (head == null) {
return false;
}

Node first = head;
Node second = head;

while (second != null) {
first = first.next; //first指针走一步
second = second.next.next; //second指针走两步

if (first == second) { //一旦两个指针相遇，说明链表是有环的
return true;
}
}

return false;
}

class Node {
//注：此处的两个成员变量权限不能为private，因为private的权限是仅对本类访问。
int data; //数据域
Node next;//指针域

public Node(int data) {
this.data = data;
}
}

public static void main(String[] args) {
LinkList list = new LinkList();
//向LinkList中添加数据
for (int i = 0; i < 4; i++) {
list.add(i);
}

list.add(list.head); //将头结点添加到链表当中，于是，单链表就有环了。备注：此时得到的这个环的结构，是下面的第8小节中图1的那种结构。
list.print(list.head);
System.out.println(list.hasCycle(list.head));
}
}

二叉树
package com.gzl.test;

import java.util.Stack;

public class BinaryTree {
/**
* 二叉树的节点数据结构
* @author WWX
*/
private class TreeNode{
private int key=0;
private String data=null;
private boolean isVisted=false;
private TreeNode leftChild=null;
private TreeNode rightChild=null;

public TreeNode(){}

/**
* @param key 层序编码
* @param data 数据域
*/
public TreeNode(int key,String data){
this.key=key;
this.data=data;
this.leftChild=null;
this.rightChild=null;
}
}

private TreeNode root=null;

public BinaryTree(){
root=new TreeNode(1,"rootNode(A)");
}

/**
* 创建一棵二叉树
* <pre>
* A
* B C
* D E F
* </pre>
* @param root
* @author WWX
*/
public void createBinTree(TreeNode root){
TreeNode newNodeB = new TreeNode(2,"B");
TreeNode newNodeC = new TreeNode(3,"C");
TreeNode newNodeD = new TreeNode(4,"D");
TreeNode newNodeE = new TreeNode(5,"E");
TreeNode newNodeF = new TreeNode(6,"F");
root.leftChild=newNodeB;
root.rightChild=newNodeC;
root.leftChild.leftChild=newNodeD;
root.leftChild.rightChild=newNodeE;
root.rightChild.rightChild=newNodeF;
}

public boolean isEmpty(){
return root==null;
}

//树的高度
public int height(){
return height(root);
}

//节点个数
public int size(){
return size(root);
}

private int height(TreeNode subTree){
if(subTree==null)
return 0;//递归结束：空树高度为0
else{
int i=height(subTree.leftChild);
int j=height(subTree.rightChild);
return (i<j)?(j+1):(i+1);
}
}

private int size(TreeNode subTree){
if(subTree==null){
return 0;
}else{
return 1+size(subTree.leftChild)
+size(subTree.rightChild);
}
}

//返回双亲结点
public TreeNode parent(TreeNode element){
return (root==null|| root==element)?null:parent(root, element);
}

public TreeNode parent(TreeNode subTree,TreeNode element){
if(subTree==null)
return null;
if(subTree.leftChild==element||subTree.rightChild==element)
//返回父结点地址
return subTree;
TreeNode p;
//现在左子树中找，如果左子树中没有找到，才到右子树去找
if((p=parent(subTree.leftChild, element))!=null)
//递归在左子树中搜索
return p;
else
//递归在右子树中搜索
return parent(subTree.rightChild, element);
}

public TreeNode getLeftChildNode(TreeNode element){
return (element!=null)?element.leftChild:null;
}

public TreeNode getRightChildNode(TreeNode element){
return (element!=null)?element.rightChild:null;
}

public TreeNode getRoot(){
return root;
}

//在释放某个结点时，该结点的左右子树都已经释放，
//所以应该采用后续遍历，当访问某个结点时将该结点的存储空间释放
public void destroy(TreeNode subTree){
//删除根为subTree的子树
if(subTree!=null){
//删除左子树
destroy(subTree.leftChild);
//删除右子树
destroy(subTree.rightChild);
//删除根结点
subTree=null;
}
}

public void traverse(TreeNode subTree){
System.out.println("key:"+subTree.key+"--name:"+subTree.data);;
traverse(subTree.leftChild);
traverse(subTree.rightChild);
}

//前序遍历
public void preOrder(TreeNode subTree){
if(subTree!=null){
visted(subTree);
preOrder(subTree.leftChild);
preOrder(subTree.rightChild);
}
}

//中序遍历
public void inOrder(TreeNode subTree){
if(subTree!=null){
inOrder(subTree.leftChild);
visted(subTree);
inOrder(subTree.rightChild);
}
}

//后续遍历
public void postOrder(TreeNode subTree) {
if (subTree != null) {
postOrder(subTree.leftChild);
postOrder(subTree.rightChild);
visted(subTree);
}
}

//前序遍历的非递归实现
public void nonRecPreOrder(TreeNode p){
Stack<TreeNode> stack=new Stack<TreeNode>();
TreeNode node=p;
while(node!=null||stack.size()>0){
while(node!=null){
visted(node);
stack.push(node);
node=node.leftChild;
}
while(stack.size()>0){
node=stack.pop();
node=node.rightChild;
}
}
}

//中序遍历的非递归实现
public void nonRecInOrder(TreeNode p){
Stack<TreeNode> stack =new Stack<BinaryTree.TreeNode>();
TreeNode node =p;
while(node!=null||stack.size()>0){
//存在左子树
while(node!=null){
stack.push(node);
node=node.leftChild;
}
//栈非空
if(stack.size()>0){
node=stack.pop();
visted(node);
node=node.rightChild;
}
}
}

//后序遍历的非递归实现
public void noRecPostOrder(TreeNode p){
Stack<TreeNode> stack=new Stack<BinaryTree.TreeNode>();
TreeNode node =p;
while(p!=null){
//左子树入栈
for(;p.leftChild!=null;p=p.leftChild){
stack.push(p);
}
//当前结点无右子树或右子树已经输出
while(p!=null&&(p.rightChild==null||p.rightChild==node)){
visted(p);
//纪录上一个已输出结点
node =p;
if(stack.empty())
return;
p=stack.pop();
}

cd99
//处理右子树
stack.push(p);
p=p.rightChild;
}
}
public void visted(TreeNode subTree){
subTree.isVisted=true;
System.out.println("key:"+subTree.key+"--name:"+subTree.data);;
}

//测试
public static void main(String[] args) {
BinaryTree bt = new BinaryTree();
bt.createBinTree(bt.root);
System.out.println("the size of the tree is " + bt.size());
System.out.println("the height of the tree is " + bt.height());

System.out.println("*******(前序遍历)[ABDECF]遍历*****************");
bt.preOrder(bt.root);

System.out.println("*******(中序遍历)[DBEACF]遍历*****************");
bt.inOrder(bt.root);

System.out.println("*******(后序遍历)[DEBFCA]遍历*****************");
bt.postOrder(bt.root);

System.out.println("***非递归实现****(前序遍历)[ABDECF]遍历*****************");
bt.nonRecPreOrder(bt.root);

System.out.println("***非递归实现****(中序遍历)[DBEACF]遍历*****************");
bt.nonRecInOrder(bt.root);

System.out.println("***非递归实现****(后序遍历)[DEBFCA]遍历*****************");
bt.noRecPostOrder(bt.root);
}
}