数据结构学习第二天＜反转链表＞＜链表删除节点＞＜栈和队列＞＜两个栈实现队列＞＜两个队列实现栈＞＜递归求最大值><哈希表>
反转链表
package Demo02;
import java.util.ArrayList;
import java.util.List;
public class Code01_ReverseList {
public static class Node {
public int value;
public Node next;
public Node(int data) {
value = data;
}
}
public static class DoubleNode {
public int value;
public DoubleNode last;
public DoubleNode next;
public DoubleNode(int data) {
value = data;
}
}
public static Node reverseLinkedList(Node head) {
Node pre = null;
Node next = null;
while (head != null) {
next = head.next;
head.next = pre;//往前指
pre = head;
head = next;
}
return pre;
}
public static DoubleNode reverseDoubleList(DoubleNode head) {
DoubleNode pre = null;
DoubleNode next = null;
while (head != null) {
next = head.next;
head.next = pre;//往前指
head.last = next;//往后指
pre = head;
head = next;
}
return pre;
}
public static Node testReverseLinkedList(Node head) {
if (head == null) {
return null;
}
ArrayList<Node> list = new ArrayList<>();
while (head != null) {
list.add(head);
head = head.next;
}
list.get(0).next = null;
int N = list.size();
for (int i = 1; i < N; i++) {
list.get(i).next = list.get(i - 1);
}
return list.get(N - 1);
}
public static DoubleNode testReverseDoubleList(DoubleNode head) {
if (head == null) {
return null;
}
ArrayList<DoubleNode> list = new ArrayList<>();
while (head != null) {
list.add(head);
head = head.next;
}
list.get(0).next = null;
DoubleNode pre = list.get(0);
int N = list.size();
for (int i = 1; i < N; i++) {
DoubleNode cur = list.get(i);
cur.last = null;
cur.next = pre;
pre.last = cur;
pre = cur;
}
return list.get(N - 1);
}
// for test
public static Node generateRandomLinkedList(int len, int value) {
int size = (int) (Math.random() * (len + 1));
if (size == 0) {
return null;
}
size--;
Node head = new Node((int) (Math.random() * (value + 1)));
Node pre = head;
while (size != 0) {
Node cur = new Node((int) (Math.random() * (value + 1)));
pre.next = cur;
pre = cur;
size--;
}
return head;
}
// for test
public static DoubleNode generateRandomDoubleList(int len, int value) {
int size = (int) (Math.random() * (len + 1));
if (size == 0) {
return null;
}
size--;
DoubleNode head = new DoubleNode((int) (Math.random() * (value + 1)));
DoubleNode pre = head;
while (size != 0) {
DoubleNode cur = new DoubleNode((int) (Math.random() * (value + 1)));
pre.next = cur;
cur.last = pre;
pre = cur;
size--;
}
return head;
}
// for test
public static List<Integer> getLinkedListOriginOrder(Node head) {
List<Integer> ans = new ArrayList<>();
while (head != null) {
ans.add(head.value);
head = head.next;
}
return ans;
}
// for test
public static boolean checkLinkedListReverse(List<Integer> origin, Node head) {
for (int i = origin.size() - 1; i >= 0; i--) {
if (!origin.get(i).equals(head.value)) {
return false;
}
head = head.next;
}
return true;
}
// for test
public static List<Integer> getDoubleListOriginOrder(DoubleNode head) {
List<Integer> ans = new ArrayList<>();
while (head != null) {
ans.add(head.value);
head = head.next;
}
return ans;
}
// for test
public static boolean checkDoubleListReverse(List<Integer> origin, DoubleNode head) {
DoubleNode end = null;
for (int i = origin.size() - 1; i >= 0; i--) {
if (!origin.get(i).equals(head.value)) {
return false;
}
end = head;
head = head.next;
}
for (int i = 0; i < origin.size(); i++) {
if (!origin.get(i).equals(end.value)) {
return false;
}
end = end.last;
}
return true;
}
public static void f(Node head) {
head = head.next;
}
// for test
public static void main(String[] args) {
int len = 50;
int value = 100;
int testTime = 100000;
System.out.println("test begin!");
for (int i = 0; i < testTime; i++) {
Node node1 = generateRandomLinkedList(len, value);
List<Integer> list1 = getLinkedListOriginOrder(node1);
node1 = reverseLinkedList(node1);
if (!checkLinkedListReverse(list1, node1)) {
System.out.println("Oops1!");
}
Node node2 = generateRandomLinkedList(len, value);
List<Integer> list2 = getLinkedListOriginOrder(node2);
node2 = testReverseLinkedList(node2);
if (!checkLinkedListReverse(list2, node2)) {
System.out.println("Oops2!");
}
DoubleNode node3 = generateRandomDoubleList(len, value);
List<Integer> list3 = getDoubleListOriginOrder(node3);
node3 = reverseDoubleList(node3);
if (!checkDoubleListReverse(list3, node3)) {
System.out.println("Oops3!");
}
DoubleNode node4 = generateRandomDoubleList(len, value);
List<Integer> list4 = getDoubleListOriginOrder(node4);
node4 = reverseDoubleList(node4);
if (!checkDoubleListReverse(list4, node4)) {
System.out.println("Oops4!");
}
}
System.out.println("test finish!");
}
}
链表删除节点
单向链表删除头结点后，head指向第二个时，即便头结点没有断连（只有1指向2，没有2指向1，2顺着能找到3，4...但找不到1），内存也会释放，C++不行（必须调用释放函数），双向链表则不会（2有指向1，能找到1）
package Demo02;
public class Code02_DeleteGivenValue {
public static class Node {
public int value;
public Node next;
public Node(int data) {
this.value = data;
}
}
public static Node removeValue(Node head, int num) {
while (head != null) {
if (head.value != num) {
break;
}
head = head.next;
}
// head来到 第一个不需要删的位置
Node pre = head;
Node cur = head;
//
while (cur != null) {
if (cur.value == num) {
pre.next = cur.next;
} else {
pre = cur;
}
cur = cur.next;
}
return head;
}
}
栈和队列
栈：先进后出
队列：先进先出
双向链表实现
package Demo02;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
public class Code03_DoubleEndsQueueToStackAndQueue {
public static class Node<T> {
public T value;
public Node<T> last;
public Node<T> next;
public Node(T data) {
value = data;
}
}
public static class DoubleEndsQueue<T> {
public Node<T> head;
public Node<T> tail;
public void addFromHead(T value) {//头部加节点
Node<T> cur = new Node<T>(value);
if (head == null) {
head = cur;
tail = cur;
} else {
cur.next = head;
head.last = cur;
head = cur;
}
}
public void addFromBottom(T value) {//尾部加节点
Node<T> cur = new Node<T>(value);
if (head == null) {
head = cur;
tail = cur;
} else {
cur.last = tail;
tail.next = cur;
tail = cur;
}
}
public T popFromHead() {//头部弹出节点
if (head == null) {
return null;
}
Node<T> cur = head;
if (head == tail) {
head = null;
tail = null;
} else {
head = head.next;
cur.next = null;
head.last = null;
}
return cur.value;
}
public T popFromBottom() {//尾部弹出节点
if (head == null) {
return null;
}
Node<T> cur = tail;
if (head == tail) {
head = null;
tail = null;
} else {
tail = tail.last;
tail.next = null;
cur.last = null;
}
return cur.value;
}
public boolean isEmpty() {
return head == null;
}
}
public static class MyStack<T> {//栈
private DoubleEndsQueue<T> queue;
public MyStack() {
queue = new DoubleEndsQueue<T>();
}
public void push(T value) {
queue.addFromHead(value);
}//头部压入
public T pop() {
return queue.popFromHead();
}//头部弹出
public boolean isEmpty() {
return queue.isEmpty();
}
}
public static class MyQueue<T> {//队列
private DoubleEndsQueue<T> queue;
public MyQueue() {
queue = new DoubleEndsQueue<T>();
}
public void push(T value) {
queue.addFromHead(value);
}//头部压入
public T poll() {
return queue.popFromBottom();
}//尾部弹出
public boolean isEmpty() {
return queue.isEmpty();
}
}
public static boolean isEqual(Integer o1, Integer o2) {
if (o1 == null && o2 != null) {
return false;
}
if (o1 != null && o2 == null) {
return false;
}
if (o1 == null && o2 == null) {
return true;
}
return o1.equals(o2);
}
public static void main(String[] args) {
int oneTestDataNum = 100;
int value = 10000;
int testTimes = 100000;
for (int i = 0; i < testTimes; i++) {
MyStack<Integer> myStack = new MyStack<>();
MyQueue<Integer> myQueue = new MyQueue<>();
Stack<Integer> stack = new Stack<>();
Queue<Integer> queue = new LinkedList<>();
for (int j = 0; j < oneTestDataNum; j++) {
int nums = (int) (Math.random() * value);
if (stack.isEmpty()) {
myStack.push(nums);
stack.push(nums);
} else {
if (Math.random() < 0.5) {
myStack.push(nums);
stack.push(nums);
} else {
if (!isEqual(myStack.pop(), stack.pop())) {
System.out.println("oops!");
}
}
}
int numq = (int) (Math.random() * value);
if (stack.isEmpty()) {
myQueue.push(numq);
queue.offer(numq);
} else {
if (Math.random() < 0.5) {
myQueue.push(numq);
queue.offer(numq);
} else {
if (!isEqual(myQueue.poll(), queue.poll())) {
System.out.println("oops!");
}
}
}
}
}
System.out.println("finish!");
}
}
数组实现（固定大小）
栈容易实现
package Demo02;
public class Code04_RingArray {
public static class MyQueue {
private int[] arr;
private int pushi;
private int polli;
private int size;
private final int limit;
public MyQueue(int limit) {
arr = new int[limit];
pushi = 0;
polli = 0;
size = 0;
this.limit = limit;
}
public void push(int value) {
if (size == limit) {
throw new RuntimeException("栈满了，不能再加了");
}
size++;
arr[pushi] = value;
pushi = nextIndex(pushi);
}
public int pop() {
if (size == 0) {
throw new RuntimeException("栈空了，不能再拿了");
}
size--;
int ans = arr[polli];
polli = nextIndex(polli);
return ans;
}
public boolean isEmpty() {
return size == 0;
}
// 如果现在的下标是i，返回下一个位置
private int nextIndex(int i) {
return i < limit - 1 ? i + 1 : 0;
}
}
}
在实现基本功能基础上再实现返回栈中最小元素
pop push getMin时间复杂度都是O（1）
package Demo02;
import java.util.Stack;
public class Code05_GetMinStack {
public static class MyStack1 {
private Stack<Integer> stackData;
private Stack<Integer> stackMin;
public MyStack1() {
this.stackData = new Stack<Integer>();
this.stackMin = new Stack<Integer>();
}
public void push(int newNum) {
if (this.stackMin.isEmpty()) {
this.stackMin.push(newNum);
} else if (newNum <= this.getmin()) {//当前数小于等于最小栈栈顶，压入，否则不压入
this.stackMin.push(newNum);
}
this.stackData.push(newNum);
}
public int pop() {
if (this.stackData.isEmpty()) {
throw new RuntimeException("Your stack is empty.");
}
int value = this.stackData.pop();
if (value == this.getmin()) {
this.stackMin.pop();
}
return value;
}
public int getmin() {
if (this.stackMin.isEmpty()) {
throw new RuntimeException("Your stack is empty.");
}
return this.stackMin.peek();
}
}
public static class MyStack2 {
private Stack<Integer> stackData;
private Stack<Integer> stackMin;
public MyStack2() {
this.stackData = new Stack<Integer>();
this.stackMin = new Stack<Integer>();
}
public void push(int newNum) {
if (this.stackMin.isEmpty()) {
this.stackMin.push(newNum);
} else if (newNum < this.getmin()) {//当前的数小于最小栈的栈顶
this.stackMin.push(newNum);//最小栈压入当前数
} else {
int newMin = this.stackMin.peek();//否则最小栈重复压入栈顶
this.stackMin.push(newMin);
}
this.stackData.push(newNum);//Data栈正常压入
}
public int pop() {
if (this.stackData.isEmpty()) {
throw new RuntimeException("Your stack is empty.");
}
this.stackMin.pop();//弹出最小数
return this.stackData.pop();//同步弹出Data栈顶
}
public int getmin() {
if (this.stackMin.isEmpty()) {
throw new RuntimeException("Your stack is empty.");
}
return this.stackMin.peek();
}
}
public static void main(String[] args) {
MyStack1 stack1 = new MyStack1();
stack1.push(3);
System.out.println(stack1.getmin());
stack1.push(4);
System.out.println(stack1.getmin());
stack1.push(1);
System.out.println(stack1.getmin());
System.out.println(stack1.pop());
System.out.println(stack1.getmin());
System.out.println("=============");
MyStack1 stack2 = new MyStack1();
stack2.push(3);
System.out.println(stack2.getmin());
stack2.push(4);
System.out.println(stack2.getmin());
stack2.push(1);
System.out.println(stack2.getmin());
System.out.println(stack2.pop());
System.out.println(stack2.getmin());
}
}
两个栈实现队列
package Demo02;
import java.util.Stack;
public class Code06_TwoStacksImplementQueue {
public static class TwoStacksQueue {
public Stack<Integer> stackPush;
public Stack<Integer> stackPop;
public TwoStacksQueue() {
stackPush = new Stack<Integer>();
stackPop = new Stack<Integer>();
}
// push栈向pop栈倒入数据
private void pushToPop() {
if (stackPop.empty()) {//原则1 必须POP栈为空的时候
while (!stackPush.empty()) {//原则2 Push栈一定要倒空才能停
stackPop.push(stackPush.pop());//一个进一个出
}
}
}
public void add(int pushInt) {
stackPush.push(pushInt);
pushToPop();//先看看能不能导，不妨碍
}
public int poll() {
if (stackPop.empty() && stackPush.empty()) {
throw new RuntimeException("Queue is empty!");
}
pushToPop();//先看看能不能导，不妨碍
return stackPop.pop();
}
public int peek() {
if (stackPop.empty() && stackPush.empty()) {
throw new RuntimeException("Queue is empty!");
}
pushToPop();//先看看能不能导，不妨碍
return stackPop.peek();
}
}
public static void main(String[] args) {
TwoStacksQueue test = new TwoStacksQueue();
test.add(1);
test.add(2);
test.add(3);
System.out.println(test.peek());
System.out.println(test.poll());
System.out.println(test.peek());
System.out.println(test.poll());
System.out.println(test.peek());
System.out.println(test.poll());
}
}
两个队列实现栈
package Demo02;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
public class Code07_TwoQueueImplementStack {
public static class TwoQueueStack<T> {
public Queue<T> queue;
public Queue<T> help;
public TwoQueueStack() {
queue = new LinkedList<>();
help = new LinkedList<>();
}
public void push(T value) {
queue.offer(value);
}
public T poll() {
while (queue.size() > 1) {
help.offer(queue.poll());
}
T ans = queue.poll();
Queue<T> tmp = queue;
queue = help;
help = tmp;
return ans;
}
public T peek() {
while (queue.size() > 1) {
help.offer(queue.poll());
}
T ans = queue.poll();
help.offer(ans);
Queue<T> tmp = queue;
queue = help;
help = tmp;
return ans;
}
public boolean isEmpty() {
return queue.isEmpty();
}
}
public static void main(String[] args) {
System.out.println("test begin");
TwoQueueStack<Integer> myStack = new TwoQueueStack<>();
Stack<Integer> test = new Stack<>();
int testTime = 1000000;
int max = 1000000;
for (int i = 0; i < testTime; i++) {
if (myStack.isEmpty()) {
if (!test.isEmpty()) {
System.out.println("Oops");
}
int num = (int) (Math.random() * max);
myStack.push(num);
test.push(num);
} else {
if (Math.random() < 0.25) {
int num = (int) (Math.random() * max);
myStack.push(num);
test.push(num);
} else if (Math.random() < 0.5) {
if (!myStack.peek().equals(test.peek())) {
System.out.println("Oops");
}
} else if (Math.random() < 0.75) {
if (!myStack.poll().equals(test.pop())) {
System.out.println("Oops");
}
} else {
if (myStack.isEmpty() != test.isEmpty()) {
System.out.println("Oops");
}
}
}
}
System.out.println("test finish!");
}
}
递归求最大值
复杂度：T(N)=a*T(N/b)+O(N^d)
a子函数个数 b几分 d剩下行为复杂度因子
1.log b a >d O(N^log b a)
2.log b a <d O(N^d) 常见a=b O(1)
3.log b a =d O(N^d *log N)
package Demo02;
public class Code08_GetMax {
// 求arr中的最大值
public static int getMax(int[] arr) {
return process(arr, 0, arr.length - 1);
}
// arr[L..R]范围上求最大值 L ... R N
public static int process(int[] arr, int L, int R) {
if (L == R) { // arr[L..R]范围上只有一个数，直接返回，base case
return arr[L];
}
int mid = L + ((R - L) >> 1); // 中点 1
int leftMax = process(arr, L, mid);
int rightMax = process(arr, mid + 1, R);
return Math.max(leftMax, rightMax);
}
}
哈希表
package Demo02;
import java.util.HashMap;
import java.util.HashSet;
import java.util.TreeMap;
public class HashMapAndSortedMap {
public static class Node{
public int value;
public Node(int v) {
value = v;
}
}
public static void main(String[] args) {
// UnSortedMap C++里的哈希表
HashMap<Integer, String> map = new HashMap<>();//K-V
map.put(1000000, "我是1000000");
map.put(2, "我是2");
map.put(3, "我是3");
map.put(4, "我是4");
map.put(5, "我是5");
map.put(6, "我是6");
map.put(1000000, "我是1000001");
System.out.println(map.containsKey(1));//有无加入1的记录
System.out.println(map.containsKey(10));
System.out.println(map.get(4));//查Value
System.out.println(map.get(10));//无记录返回null
map.put(4, "他是4");//更新V
System.out.println(map.get(4));
map.remove(4);//除去
System.out.println(map.get(4));//null
// key
HashSet<String> set = new HashSet<>();
set.add("abc");
set.contains("abc");//是否存在
set.remove("abc");
// 哈希表，增、删、改、查，在使用时，复杂度O（1）
System.out.println("=====================");
int a = 100000;
int b = 100000;
System.out.println(a == b);
Integer c = 100000;
Integer d = 100000;
System.out.println(c.equals(d));//==引用传递 equal比较值
Integer e = 127; // - 128 ~ 127 此范围内是值传递
Integer f = 127;
System.out.println(e == f);
//哈西表里一律值传递
HashMap<Node, String> map2 = new HashMap<>();
Node node1 = new Node(1);
Node node2 = node1;
map2.put(node1, "我是node1");
map2.put(node2, "我是node1");
System.out.println(map2.size());//1 非基础类型K 引用传递
System.out.println("======================");
//有序表（按序组织）
TreeMap<Integer, String> treeMap = new TreeMap<>();
treeMap.put(3, "我是3");
treeMap.put(4, "我是4");
treeMap.put(8, "我是8");
treeMap.put(5, "我是5");
treeMap.put(7, "我是7");
treeMap.put(1, "我是1");
treeMap.put(2, "我是2");
System.out.println(treeMap.containsKey(1));
System.out.println(treeMap.containsKey(10));
System.out.println(treeMap.get(4));
System.out.println(treeMap.get(10));
treeMap.put(4, "他是4");
System.out.println(treeMap.get(4));
treeMap.remove(4);
System.out.println(treeMap.get(4));
System.out.println(treeMap.firstKey());//最小的K
System.out.println(treeMap.lastKey());
// <= 4
System.out.println(treeMap.floorKey(4));//<=4 离4最近的K
// >= 4
System.out.println(treeMap.ceilingKey(4));//>=4 离4最近的K
// O(logN)
}
}
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