package jz.bm;
import java.util.*;
public class bm4 {
/**
* BM42 用两个栈实现队列
*/
Stack<Integer> stack1 = new Stack<>();
Stack<Integer> stack2 = new Stack<>();
public void push(int node) {
stack1.push(node);
}
public int pop() {
while (!stack1.isEmpty()) {
stack2.push(stack1.pop());
}
int res = stack2.pop();
while (!stack2.isEmpty()) {
stack1.push(stack2.pop());
}
return res;
}
/**
* BM43 包含min函数的栈
*/
Stack<Integer> stack42 = new Stack<>();
Stack<Integer> stack42min = new Stack<>();
public void push42(int node) {
stack42.push(node);
if (stack42min.isEmpty()) {
stack42min.push(node);
} else {
if (node < stack42min.peek()) {
stack42min.push(node);
} else {
stack42min.push(stack42min.peek());
}
}
}
public void pop42() {
stack42.pop();
stack42min.pop();
}
public int top42() {
return stack42.peek();
}
public int min42() {
return stack42min.peek();
}
/**
* BM44 有效括号序列
*/
public boolean isValid (String s) {
if (s.length() == 0) {
return true;
}
Stack<Character> stack = new Stack<>();
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '(') {
stack.push(')');
} else if (s.charAt(i) == '{') {
stack.push('}');
} else if (s.charAt(i) == '[') {
stack.push(']');
} else {
if (stack.size() != 0 && stack.peek() == s.charAt(i)) {
stack.pop();
} else {
stack.push(s.charAt(i));
}
}
}
return stack.size() <= 0;
}
/**
* BM45 滑动窗口的最大值
*/
public ArrayList<Integer> maxInWindows (int[] num, int size) {
ArrayList<Integer> res = new ArrayList<>();
if (size > num.length || size == 0) {
return res;
}
PriorityQueue<Integer> priorityQueue = new PriorityQueue<>((o1, o2) -> o2 - o1);
//初始化
for (int i = 0; i < size; i++) {
priorityQueue.add(num[i]);
}
res.add(priorityQueue.peek());
for (int i = size; i < num.length; i++) {
priorityQueue.remove(num[i - size]);
priorityQueue.add(num[i]);
res.add(priorityQueue.peek());
}
return res;
}
/**
* BM46 最小的K个数
*/
public ArrayList<Integer> GetLeastNumbers_Solution (int[] input, int k) {
ArrayList<Integer> res = new ArrayList<>();
if (input.length == 0) {
return res;
}
PriorityQueue<Integer> queue = new PriorityQueue<>();
for (int i = 0; i < input.length; i++) {
queue.add(input[i]);
}
for (int i = 0; i < k; i++) {
res.add(queue.peek());
queue.poll();
}
return res;
}
/**
* BM47 寻找第K大
*/
public int findKth (int[] a, int n, int K) {
PriorityQueue<Integer> queue = new PriorityQueue<>((o1, o2) -> o2 - o1);
for (int i = 0; i < n; i++) {
queue.add(a[i]);
}
for (int i = 0; i < K - 1; i++) {
queue.poll();
}
return queue.peek();
}
/**
* BM48 数据流中的中位数
*/
ArrayList<Integer> list48 = new ArrayList<>();
public void Insert(Integer num) {
if (list48.size() == 0) {
list48.add(num);
} else {
//插入排序
int j = 0;
for (; j < list48.size(); j++) {
if (num < list48.get(j)) {
break;
}
}
list48.add(j, num);
}
}
public Double GetMedian() {
int n = list48.size();
if (n % 2 == 0) {
double a = list48.get(n / 2 - 1);
double b = list48.get(n / 2);
return (a + b) / 2.0;
} else {
return (double) list48.get(n / 2);
}
}
/**
* BM49 表达式求值
*/
public int solve (String s) {
return recursion(s, 0).get(0);
}
private ArrayList<Integer> recursion(String s, int index) {
Stack<Integer> stack = new Stack<>();
int num = 0; //每一个因子
int i;
char op = '+'; //默认为+，相当于 0 + 表达式
for (i = index; i < s.length(); i++) {
if (s.charAt(i) >= '0' && s.charAt(i) <= '9') {
num = num * 10 + s.charAt(i) - '0';
//不是最后一个字符，继续判断是否为数字
if (i != s.length() - 1) {
continue;
}
}
//遇到（将括号内当成一个数字
if (s.charAt(i) == '(') {
ArrayList<Integer> res = recursion(s, i + 1);
num = res.get(0);
i = res.get(1);
if (i != s.length() - 1) {
continue;
}
}
//数字取完需要计算
//当前数字前面的操作符
switch (op) {
case '+' :
stack.push(num);
break;
case '-':
stack.push(-num);
break;
case '*':
int temp = stack.pop();
stack.push(temp * num);
break;
}
num = 0;
//遇到）结束当前表达式
if (s.charAt(i) == ')') {
break;
} else {
op = s.charAt(i);
}
}
int sum = 0;
while (!stack.isEmpty()) {
sum += stack.pop();
}
//记录当前表达式的结果和在字符串的位置
ArrayList<Integer> list = new ArrayList<>();
list.add(sum);
list.add(i);
return list;
}
}
Algorithm Exercise (3): Niuke Online Programming 04 Heap/Stack/Queue
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Origin blog.csdn.net/weixin_42774617/article/details/131969007
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