P2201 數列編輯器（對頂棧）

include<bits/stdc++.h>

using namespace std;

define x first

define y second

typedef pair<int,int> PII;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef vector VS;
typedef vector VI;
typedef vector<vector> VVI;
vector vx;
inline int mp(int x) {return upper_bound(vx.begin(),vx.end(),x)-vx.begin();}
inline int log_2(int x) {return 31-__builtin_clz(x);}
inline int popcount(int x) {return __builtin_popcount(x);}
inline int lowbit(int x) {return x&-x;}
const int N = 1e6+10,suf = -2139062144;
int A[N],B[N],s[N],f[N];
int tA = 0, tB = 0;
void solve()
{
//用A儲存從開始到游標的棧,B儲存游標後到結尾的序列
//s[i]為字首和,f[i]為字首和最大值
f[0] = suf;
int n;
cin>>n;
for(int i=1;i<=n;++i)
{
char op;
cin>>op;
if(op == 'I')
{
int x;
cin>>x;
A[++tA] = x;
s[tA] = s[tA-1] + x;
f[tA] = max(f[tA-1],s[tA]);
}
else if(op == 'D') --tA;
else if(op == 'L')
{
B[++tB] = A[tA--];
}
else if(op == 'R')
{
int x = B[tB--];
A[++tA] = x;
s[tA] = s[tA-1] + x;
f[tA] = max(f[tA-1],s[tA]);
}
else
{
int x;
cin>>x;
cout<<f[x]<<'\n';
}
}
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int T = 1;
//cin>>T;
while(T--)
{
solve();
}
}