hdu 1024 最大m段不相交线段和

[题目传送门](http://acm.hdu.edu.cn/showproblem.php?pid=1024)//res tp hdu

数据范围1e6，若是开二维会爆
考虑用滚动数组优化

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define per(i,a,b) for(int i = (a);i>=(b);--i)
#define fo(i,a,b) for(int i =(a);i<(b);++i)
#define de(x) cout<<#x<<" = "<<x<<endl;
#define endl '\n'
#define ls(p) ((p)<<1)
#define rs(p) (((p)<<1)|1)
using namespace std;
typedef long long ll;
const int mn = 1e6+10;
// search m seg to make the sum of them max
//1e6, more than one test
ll arr[mn];
ll dp[mn],pre[mn];
// 滚动数组优化二维dp
int main(){
	int n,m;
	while(scanf("%d %d",&m,&n)!=EOF){
		rep(i,1,n) scanf("%lld",&arr[i]);
		//dp[i][j] = max(dp[i][j-1]+arr[j],max(dp[i-1][k])+arr[j]) (1 <=k<=j-1)
		ll MAX;
		rep(i,1,n) dp[i] = pre[i] = 0;
		rep(i,1,m){
			MAX = -1e9; // max in [1,j-1]
			rep(j,i,n){
				dp[j] = max(dp[j-1],pre[j-1])+arr[j];
				pre[j-1] = MAX;
				MAX = max(MAX,dp[j]);
			}
		}
		printf("%lld\n",MAX);
	}
}