hdu 1540 Tunnel Warfare 线段树 单点更新，查询区间长度，区间合并

题目链接:

http://acm.hdu.edu.cn/showproblem.php?pid=1540

题意:

给你一个区间，有三个操作，使的一个村庄毁灭，使的上一个毁灭的村庄复活，查询这个村庄所在最长区间

题解:

区间合并的线段树，单点修改，记录从左边的最大值，右边的最大值，区间的最大值
然后每次更新

代码:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define MS(a) memset(a,0,sizeof(a))
#define MP make_pair
#define PB push_back
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
inline ll read(){
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
//////////////////////////////////////////////////////////////////////////
const int maxn = 1e5+10;

struct node{
    int l,r,lm,rm,mm,len;
}tree[maxn<<2];

void pushup(int rt){
    tree[rt].lm = tree[rt<<1].lm;
    tree[rt].rm = tree[rt<<1|1].rm;
    tree[rt].mm = max(max(tree[rt<<1].mm,tree[rt<<1|1].mm),tree[rt<<1].rm+tree[rt<<1|1].lm);
    if(tree[rt<<1].lm == tree[rt<<1].len) tree[rt].lm = tree[rt<<1].lm + tree[rt<<1|1].lm;
    if(tree[rt<<1|1].rm == tree[rt<<1|1].len) tree[rt].rm = tree[rt<<1].rm+tree[rt<<1|1].rm;
}

void build(int rt,int l,int r){
    tree[rt].l = l, tree[rt].r = r;
    tree[rt].lm = tree[rt].rm = tree[rt].mm = tree[rt].len = r-l+1;
    if(l != r){
        int mid = (l+r)/2;
        build(rt<<1,l,mid);
        build(rt<<1|1,mid+1,r);
        pushup(rt);
    }
}

void update(int rt,int p,int x){
    int L = tree[rt].l, R = tree[rt].r;
    if(L == R) { 
        tree[rt].lm=tree[rt].rm=tree[rt].mm = x;
        return ;
    }

    int mid = (L+R)/2;
    if(p <= mid) update(rt<<1,p,x);
    else update(rt<<1|1,p,x);
    pushup(rt);
}

ll query(int rt,int p){
    int L = tree[rt].l, R = tree[rt].r;
    if(L==R || tree[rt].mm==0 || tree[rt].mm==tree[rt].len)
        return tree[rt].mm;
    int mid = (L+R)/2;
    if(p<=mid){
        if(p >= tree[rt<<1].r - tree[rt<<1].rm + 1){
            return query(rt<<1,p) + query(rt<<1|1,mid+1);
        }else{
            return query(rt<<1,p);
        }
    }else{
        if(p <= tree[rt<<1|1].l+tree[rt<<1|1].lm-1){
            return query(rt<<1|1,p) + query(rt<<1,mid);
        }else{
            return query(rt<<1|1,p);
        }
    }
}

int main(){
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF){
        stack<int> k;
        build(1,1,n);
        for(int i=0; i<m; i++){
            char op; scanf(" %c",&op);
            int t;
            if(op == 'D'){
                scanf("%d",&t);
                update(1,t,0);
                k.push(t);
            }else if(op == 'Q'){
                scanf("%d",&t); 
                printf("%I64d
",query(1,t));
            }else{
                update(1,k.top(),1);
                k.pop();
            }
        }
    }

    return 0;
}