https://codeforces.com/contest/1155/problem/D
题解:DP
1、最大连续区间和=当前i前缀和-min{0-i-1前缀和};
2、定义三个数组,分别为:
1、从没有加x;
2、已经x并且持续到当前i位置;
3、已经加x但是当前i位置不加x;
3、long long 是必要的;
/*
*@Author: STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=300000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const ll INF = 0x3f3f3f3f3f3f;
int t,n,m,k,p,l,r,u,v;
ll ans,cnt,flag,temp,sum[N];
ll a[N];
ll dp[3][N];
char str;
struct node{};
int main()
{
#ifdef DEBUG
freopen("input.in", "r", stdin);
//freopen("output.out", "w", stdout);
#endif
//ios::sync_with_stdio(false);
//cin.tie(0);
//cout.tie(0);
//scanf("%d",&t);
//while(t--){
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++){
scanf("%I64d",&a[i]);
}
ll minl= 0;
for(int i=1;i<=n;i++){
sum[i]=sum[i-1]+a[i];
dp[2][i]=max(max(dp[2][i-1]+a[i],dp[1][i-1]+a[i]),0ll);
dp[1][i]=max(max(dp[0][i-1],dp[1][i-1])+a[i]*m,0ll);
dp[0][i]=max(sum[i]-minl,0ll);
ans=max(max(dp[0][i],ans),max(dp[1][i],dp[2][i]));
minl=min(minl,sum[i]);
}
cout<<ans<<endl;
//}
#ifdef DEBUG
printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
//cout << "Hello world!" << endl;
return 0;
}