LuoguP1937 [USACO10MAR]Barn Allocation G

LuoguP1937 [USACO10MAR]Barn Allocation G

题目描述

链接

Solution

贪心的同时开个线段树判断一下可不可以放

#include<bits/stdc++.h>

using namespace std;

inline int read()
{
    int f = 1,x = 0;
    char ch;
    do
    {
        ch = getchar();
        if(ch == '-') f = -1;
    }while(ch<'0'||ch>'9');
    do
    {
        x = (x<<3) + (x<<1) + ch - '0';
        ch = getchar();
    }while(ch>='0'&&ch<='9');
    return f*x;
}

const int MAXN = 200000 + 10;

int n,m;
int a[MAXN<<2];
int T[MAXN<<2]; 
int add[MAXN<<2];

#define lc o<<1
#define rc o<<1|1

inline void build(int o,int l,int r)
{
    if(l == r)
    {
        T[o] = a[l];
        return;
    }
    int mid = (l + r) >> 1;
    build(lc,l,mid);
    build(rc,mid+1,r);
    T[o] = min(T[lc],T[rc]);
    return;
}

inline void pushdown(int o,int l,int r)
{
    int mid = (l + r) >> 1;
    add[lc] += add[o];
    add[rc] += add[o];
    T[lc] += add[o];
    T[rc] += add[o];
    add[o] = 0;
    return;
}

inline void update(int o,int L,int R,int l,int r,int v)
{
    if(L<=l&&r<=R) 
    {
        T[o] +=  v;
        add[o] += v;
        return; 
    } 
    if(L > r|| l > R) return;
    if(add[o]!=0) pushdown(o,l,r);
    int mid = (l + r) >> 1;
    update(lc,L,R,l,mid,v);
    update(rc,L,R,mid+1,r,v);
    T[o] = min(T[lc],T[rc]);
}

inline int query(int o,int L,int R,int l,int r)
{
    if(L<=l&&r<=R) 
    {
        return T[o]; 
    } 
    if(L > r|| l > R) return 1<<30;
    if(add[o]!=0) pushdown(o,l,r);
    int mid = (l + r) >> 1;
    return min(query(lc,L,R,l,mid),query(rc,L,R,mid+1,r));
}

struct Query
{
    int l,r;
    friend bool operator < (Query a1,Query a2)
    {
        if(a1.r != a2.r) return a1.r < a2.r;
        else return a1.l > a2.l;
    }
}q[MAXN];

int main()
{
    n = read();m = read();
    for(int i=1;i<=n;i++) a[i] = read();
//    cout << " FUCK" << endl;
    build(1,1,n);
    int ans = 0;
    for(int i=1;i<=m;i++)
    {
        q[i].l = read(),q[i].r = read();
    }
    sort(q+1,q+m+1);
//    for(int i=1;i<=m;i++) cout << q[i].l << " " << q[i].r << endl;
    for(int i=1;i<=m;i++)
    {
        int v = query(1,q[i].l,q[i].r,1,n);
        //cout << v << endl;
        if(v<=0) continue;
        ans++;
        update(1,q[i].l,q[i].r,1,n,-1);
    }
    cout << ans << endl;
}