【HDU】1540 Tunnel Warfare

#include<cstdio>
#include<stack>
#define MAXN 50010
#define MAX(a,b) ((a)>(b)?(a):(b))
using namespace std;
stack<int>st;
struct node
{
int left,right;
};
node tree[MAXN<<2];
void Build(int L,int R,int rt)
{
tree[rt].left=tree[rt].right=R-L+1;
if(L!=R)
{
int mid=(L+R)>>1;
Build(L,mid,rt<<1);
Build(mid+1,R,rt<<1|1);
}
}
inline void PushUp(int mid,int L,int R,int rt)
{
tree[rt].left=tree[rt<<1].left;
tree[rt].right=tree[rt<<1|1].right;
if(tree[rt].left==mid-L+1)
tree[rt].left+=tree[rt<<1|1].left;
if(tree[rt].right==R-mid)
tree[rt].right+=tree[rt<<1].right;
}
void Update(int x,int val,int L,int R,int rt)
{
if(L==R)
tree[rt].left=tree[rt].right=val;
else
{
int mid=(L+R)>>1;
if(x<=mid)
Update(x,val,L,mid,rt<<1);
else
Update(x,val,mid+1,R,rt<<1|1);
PushUp(mid,L,R,rt);
}
}
int Query(int x,int L,int R,int rt)
{
if(L==R)
return tree[rt].left;
int mid=(L+R)>>1;
if(x<=mid)
{
if(tree[rt<<1].left==mid-L+1)
return tree[rt<<1].left+tree[rt<<1|1].left;
else if(L+tree[rt<<1].left>x)
return tree[rt<<1].left;
else if(x>mid-tree[rt<<1].right)
return tree[rt<<1].right+tree[rt<<1|1].left;
else
return Query(x,L,mid,rt<<1);
}
else
{
if(tree[rt<<1|1].right==R-mid)
return tree[rt<<1|1].right+tree[rt<<1].right;
else if(x<mid+1+tree[rt<<1|1].left)
return tree[rt<<1].right+tree[rt<<1|1].left;
else if(x>R-tree[rt<<1|1].right)
return tree[rt<<1|1].right;
else
return Query(x,mid+1,R,rt<<1|1);
}
}
int main()
{
int n,m,x;
char ch;
while(~scanf("%d%d",&n,&m))
{
Build(1,n,1);
for(;!st.empty();st.pop());
while(m--)
{
scanf(" %c",&ch);
if(ch=='D')
{
scanf("%d",&x);
st.push(x);
Update(x,0,1,n,1);
}
else if(ch=='Q')
{
scanf("%d",&x);
printf("%d\n",Query(x,1,n,1));
}
else
{
if(!st.empty())
{
Update(st.top(),1,1,n,1);
st.pop();
}
}
}
}
return 0;
}