题解 | 【模板】循环队列

//  #牛客春招刷题训练营# https://www.nowcoder.com/discuss/726480854079250432
//  我用的是向量模拟的
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

int main() {
  ios_base::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr);
  int n, q, x, top, tail;
  cin >> n >> q;
  vector<int> a(n, 0);
  top = 0;// The first expect start.//------------除非队列为空不然都指向第一个
  tail = 0;// The next of end.
  string s;
  bool is_full = 0;//--------用于当top==tail时辅助判断队列是空还是满
  while(q--){
    cin >> s;
    if (s == "push"){
      cin >> x;
      if (tail == top && is_full){
        cout << "full\n";
      }
      else{
        a[tail] = x;
        tail++;
        if (tail == n) tail = 0;//----------循环处理
        if (top == tail) is_full = 1;
      }
    }
    else if (s == "front"){
      if (top == tail && !is_full)
        cout << "empty\n";
      else
        cout << a[top] << '\n';
    }
    else{
      if (top == tail && !is_full)
        cout << "empty\n";
      else{
        cout << a[top] << '\n';
        if (top == n - 1) top = 0;//----------循环处理
        else top++;
        if (top == tail) is_full = 0;
      }
    }
  }
  return 0;
}
// 64 位输出请用 printf("%lld")