牛客练习赛91 B.魔法学院(easy version) (segment tree beats!)

完完全全就是segment tree beats的板子题

代码：

#include <bits/stdc++.h>
using namespace std;
#define PII pair<int,int>
#define fi first
#define se second
#define pb push_back
#define ll long long
#define ull unsigned long long
#define PLL pair<ll,ll>
const int N=1000010;
const int mod=1e9+7;
const int INF=0x3f3f3f3f;

#define int long long 

struct Node{
    int l,r;
    char c;
}e[N];

struct misaka{
    int l,r;
    ll sum;
    ll mi,semi;
    ll cnt;
    char c;
    char tag;
}tr[N<<4];

int n,m;
char s[N];

void push_up(int u){
    if(tr[u<<1].mi<tr[u<<1|1].mi){
        tr[u].mi=tr[u<<1].mi;
        tr[u].cnt=tr[u<<1].cnt;
        tr[u].semi=min(tr[u<<1].semi,tr[u<<1|1].mi);
    }
    else if(tr[u<<1].mi>tr[u<<1|1].mi){
        tr[u].mi=tr[u<<1|1].mi;
        tr[u].cnt=tr[u<<1|1].cnt;
        tr[u].semi=min(tr[u<<1|1].semi,tr[u<<1].mi);
    }
    else{
        tr[u].mi=tr[u<<1].mi;
        tr[u].cnt=tr[u<<1].cnt+tr[u<<1|1].cnt;
        tr[u].semi=min(tr[u<<1].semi,tr[u<<1|1].semi);
    }
    tr[u].sum=tr[u<<1].sum+tr[u<<1|1].sum;
}

void push_down(int u){
    if(tr[u].tag){
        if(tr[u<<1].mi<tr[u].tag){
            tr[u<<1].sum=tr[u<<1].sum+1ll*(tr[u].tag-tr[u<<1].mi)*tr[u<<1].cnt;
            tr[u<<1].mi=tr[u].tag;
            tr[u<<1].tag=tr[u].tag;
        }
        if(tr[u<<1|1].mi<tr[u].tag){
            tr[u<<1|1].sum=tr[u<<1|1].sum+1ll*(tr[u].tag-tr[u<<1|1].mi)*tr[u<<1|1].cnt;
            tr[u<<1|1].mi=tr[u].tag;
            tr[u<<1|1].tag=tr[u].tag;
        }
        tr[u].tag=0;
    }
}

void build(int u,int l,int r){
    if(l==r){
        tr[u]={l,r,s[l],s[l],INF,1,s[l],0};
        return;
    }
    tr[u]={l,r,0,0,0,0,0,0};
    int mid=(l+r)>>1;
    build(u<<1,l,mid);
    build(u<<1|1,mid+1,r);
    push_up(u);
}

void update(int u,int L,int R,char x){
    if(tr[u].mi>=x) return;
    if(tr[u].l>=L && tr[u].r<=R){
        if(x<tr[u].semi){
            tr[u].sum=tr[u].sum+1ll*(x-tr[u].mi)*tr[u].cnt;
            tr[u].mi=x;
            tr[u].tag=x;
            return;
        }
    }
    push_down(u);
    int mid=(tr[u].l+tr[u].r)>>1;
    if(L<=mid) update(u<<1,L,R,x);
    if(R>mid) update(u<<1|1,L,R,x);
    push_up(u);
}


signed main(){
    scanf("%lld %lld",&n,&m);
    getchar();
    scanf("%s",s+1);
    for(int i=1;i<=m;++i){
        scanf("%lld %lld %c",&e[i].l,&e[i].r,&e[i].c);
    }
    //这一步排序其实是多余的
    sort(e+1,e+1+m,[&](Node a,Node b){
            return a.c<b.c;
    });
    build(1,1,n);
    for(int i=1;i<=m;++i) update(1,e[i].l,e[i].r,e[i].c);
    printf("%lld\n",tr[1].sum);
    return 0;
}