Tunnel Warfare----hdu1540线段树

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<math.h>
#include<stack>
#include<iostream>
#define INF 0xfffffff
#define N 50100
using namespace std;

#define Lson r<<1
#define Rson r<<1|1

struct SegTree
{
    int L, R;
    int s,ls,rs;
    //s代表L--R中最大连续个数，ls代表L开始所能没有破坏的连续个数；同理rs；
    int mid()
    {
        return (L+R)>>1;
    }
    int len()
    {
        return R-L+1; 
    }
}a[N*4];

void Update(int r, int x, int op)
{
    if(a[r].L == a[r].R)
    {
        a[r].ls = a[r].rs = a[r].s = op;
        return;
    }
    if(x<=a[r].mid())
        Update(Lson, x, op);
    else
        Update(Rson, x, op);

    a[r].ls = a[Lson].ls;
    a[r].rs = a[Rson].rs;

    if(a[Lson].ls == a[Lson].len())
        a[r].ls = a[Lson].ls + a[Rson].ls;
    if(a[Rson].rs == a[Rson].len())
        a[r].rs = a[Rson].rs + a[Lson].rs;

    a[r].s = max(a[Lson].rs + a[Rson].ls, max(a[Lson].ls, a[Rson].rs));
}

void BuildSegTree(int r, int L, int R)
{
    a[r].L = L, a[r].R = R;
    a[r].ls = a[r].rs = a[r].s = a[r].len();
    if(L == R)return;
    BuildSegTree(Lson, L, a[r].mid());
    BuildSegTree(Rson, a[r].mid()+1, R);
}
int Query(int r, int x)
{
    if(a[r].s == 0)
        return 0;
    if(x < a[r].L + a[r].ls)//判断是否在左边
        return a[r].ls;
    if(x > a[r].R - a[r].rs)//判断是否在右边
        return a[r].rs;
    if(x > a[Lson].R - a[Lson].rs && x < a[Rson].L+a[Rson].ls)
        return a[Lson].rs + a[Rson].ls;

    if(x <= a[r].mid())
        return Query(Lson, x);
    else
        return Query(Rson, x);
}
int main()
{
    int n, m, x;
    char str[10];
    stack<int>Q;
    while(scanf("%d%d", &n, &m) != EOF)
    {
        BuildSegTree(1, 1, n);
        while(m--)
        {
            scanf("%s", str);
            if(str[0] == ‘D‘)
            {
                scanf("%d", &x);
                Update(1, x, 0);
                Q.push(x);
            }
            else if(str[0] == ‘Q‘)
            {
                scanf("%d", &x);
                printf("%d\n", Query(1, x));
            }
            else
            {
                Update(1, Q.top(), 1);
                Q.pop();
            }
        }
    }
    return 0;
}