【Luogu】P1868饥饿的奶牛（DP）

f[i]=f[i-1];
f[i]=max(f[i],f[x[j]-1]+y[j]-x[j]+1);

#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
inline long long read(){
    long long num=0,f=1;
    char ch=getchar();
    while(!isdigit(ch)){
        if(ch==‘-‘)    f=-1;
        ch=getchar();
    }
    while(isdigit(ch)){
        num=num*10+ch-‘0‘;
        ch=getchar();
    }
    return num*f;
}

struct Edge{
    int next,to;
}edge[1001010];
int head[3000010],num;
inline void add(int from,int to){
    edge[++num]=(Edge){head[from],to};
    head[from]=num;
}

int f[3000010];
int m;

int main(){
    int n=read();
    for(int i=1;i<=n;++i){
        int x=read(),y=read();
        add(y,x);
        m=std::max(m,y);
    }
    for(int i=1;i<=m;++i){
        f[i]=f[i-1];
        for(int s=head[i];s;s=edge[s].next){
            int x=edge[s].to;
            f[i]=std::max(f[i],f[x-1]+i-x+1);
        }
    }
    printf("%d",f[m]);
    return 0;
}