HDU 1540 Tunnel Warfare

#include<stdio.h>
#include<algorithm>
#include<stack>
#define N 50010
using namespace std;
struct node
{
    int left, right, sum, Lsum, Rsum; //sum存放与该点相连的点的总个数，Lsum存放从左端点开始向右与之相连的点的最大个数，Rsum存放从右端点开始向左与之相连的点的最大个数
}no[4*N];
void Bulid(int left, int right, int root)
{
    int mid;
    no[root].left = left;
    no[root].right = right;
    no[root].sum = no[root].Lsum = no[root].Rsum = (no[root].right-no[root].left+1); //开始时所有点相连的个数都等于其区间的长度
    if (left == right) return ;
    mid = (left+right)/2;
    Bulid(left, mid, root*2);
    Bulid(mid+1, right, root*2+1);
}
void Pushup(int root) //向上更新
{
    no[root].Lsum = no[root*2].Lsum;
    no[root].Rsum = no[root*2+1].Rsum;
    if (no[root*2].Lsum == no[root*2].right-no[root*2].left+1) //只有当左结点的Lsum与区间长度相等了才能加上右结点的部分，否则会有重复现象
        no[root].Lsum = no[root*2].Lsum + no[root*2+1].Lsum;
    if (no[root*2+1].Rsum == no[root*2+1].right-no[root*2+1].left+1)
        no[root].Rsum = no[root*2+1].Rsum + no[root*2].Rsum;
    no[root].sum = max(no[root].Lsum, max(no[root].Rsum, no[root*2].Rsum+no[root*2+1].Lsum));
}
void Update(int k, int num, int root)
{
    int mid;
    if (no[root].left == no[root].right)
    {
        no[root].Lsum = no[root].Rsum = num;
        return ;
    }
    mid = (no[root].left+no[root].right)/2;
    if (k <= mid) Update(k, num, root*2);
    else Update(k, num, root*2+1);
    Pushup(root);
}
int Query(int k, int root)
{
    int mid;
    if (no[root].sum == 0) return 0;
    if (k < no[root].left+no[root].Lsum) return no[root].Lsum;
    if (k > no[root].right-no[root].Rsum) return no[root].Rsum;
    if (k > no[root*2].right-no[root*2].Rsum && k < no[root*2+1].left+no[root*2+1].Lsum)
        return no[root*2].Rsum+no[root*2+1].Lsum;
    mid = (no[root].left+no[root].right)/2;
    if (k <= mid) return Query(k, root*2);
    else return Query(k, root*2+1);
}
int main ()
{
    int n, m, k, Sum;
    char s[10];
    stack<int>Q;
    while (scanf("%d%d", &n, &m) != EOF)
    {
        Bulid(1, n, 1);
        while (m--)
        {
            scanf("%s", s);
            if (s[0] == ‘D‘)
            {
                scanf("%d", &k);
                Update(k, 0, 1);
                Q.push(k);
            }
            else if (s[0] == ‘Q‘)
            {
                scanf("%d", &k);
                Sum = Query(k, 1);
                printf("%d\n", Sum);
            }
            else if (s[0] == ‘R‘)
            {
                Update(Q.top(), 1, 1);
                Q.pop();
            }
        }
    }
    return 0;
}