蓝桥杯学习-11栈

11栈

先进后出

例题–蓝桥19877

用数组来设置栈 1.向栈顶插入元素–top位置标记元素 2.删除栈顶元素–top指针减减 3.输出栈顶元素–输出top位置元素

使用arraylist

import java.util.ArrayList; import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc=new Scanner(System.in); ArrayList array=new ArrayList<>(); int m=sc.nextInt(); for (int i = 0; i < m; i++){ String str=sc.next(); switch (str){ case “push”: int x=sc.nextInt(); array.add(x); break; case “pop”: if (array.size()==0){ break; }else { array.remove(array.size()-1); } break; case “empty”: if (array.size()==0){ System.out.println(“YES”); }else { System.out.println(“NO”); } break; case “query”: if (array.size()==0){ System.out.println(“empty”); }else { System.out.println(array.get(array.size()-1)); } break; default: System.out.println(“error”); } } } }

使用数组

import java.io.; import java.util.; import java.math.BigInteger; public class Main { static int N = (int)(1e5+10); static int[] stk = new int[N]; static int top = 0; static void push(int x) { stk[++top] = x; } static void pop() { if(isEmpty()) return; top–; } static boolean isEmpty() { return top==0; } static void query() { if(isEmpty()) out.println(“empty”); else out.println(stk[top]); } static void solve() { int m = in.nextInt(); while(m–>0) { String op = in.next(); if(op.equals(“push”)) { int x = in.nextInt(); push(x); }else if(op.equals(“pop”)) { pop(); }else if(op.equals(“empty”)) { out.println(isEmpty()?“YES”:“NO”); }else { query(); } } } public static void main(String[] args) { solve(); out.flush(); } static FastReader in = new FastReader(); static PrintWriter out = new PrintWriter(System.out); static class FastReader { static BufferedReader br; static StringTokenizer st; FastReader() { br = new BufferedReader(new InputStreamReader(System.in)); } String next() { String str = “”; while(st==null||!st.hasMoreElements()) { try { str = br.readLine(); }catch(IOException e) { throw new RuntimeException(e); } st = new StringTokenizer(str); } return st.nextToken(); } int nextInt() { return Integer.parseInt(next()); } double nextDouble() { return Double.parseDouble(next()); } long nextLong() { return Long.parseLong(next()); } } }