P2242 公路维修问题

P2242 公路维修问题

解题思路：贪心。把相邻两个数的差值进行从大到小排序，按照差值最大的进行分割。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double lf;
typedef unsigned long long ull;
typedef pair<ll,int>P;
const int inf = 0x7f7f7f7f;
const ll INF = 1e16;
const int N = 1e6+10;
const ull base = 131;
const ll mod =  1e9+7;
const double PI = acos(-1.0);
const double eps = 1e-4;

inline int read(){
    
    int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){
    
    if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){
    
    x=x*10+ch-'0';ch=getchar();}return x*f;}
inline string readstring(){
    
    string str;char s=getchar();while(s==' '||s=='\n'||s=='\r'){
    
    s=getchar();}while(s!=' '&&s!='\n'&&s!='\r'){
    
    str+=s;s=getchar();}return str;}
int random(int n){
    
    return (int)(rand()*rand())%n;}
void writestring(string s){
    
    int n = s.size();for(int i = 0;i < n;i++){
    
    printf("%c",s[i]);}}
ll fast_power(ll a,ll p){
    
    
    ll ans = 1;
    while(p){
    
    
        if(p&1) ans = (ans*a)%mod;
        p >>= 1;
        a = (a*a)%mod;
    }
    return ans;
}


struct node{
    
    
    int num;
    int x,y;
}a[N];
int num[N];

bool cmp(node a,node b){
    
    
    return a.num > b.num;
}
int main(){
    
    
    //srand((unsigned)time(NULL));
    //freopen(  "out.txt","w",stdout);
    int n = read(),m = read();
    for(int i = 1;i <= n;i++){
    
    
        num[i] = read();
    }
    for(int i = 1;i < n;i++){
    
    
        a[i].num = num[i+1]-num[i];
        a[i].x = i;
        a[i].y = i+1;
    }
    sort(a+1,a+n,cmp);
    if(m == n){
    
    
        printf("%d\n",m);
        return 0;
    }
    vector<int>b;
    b.push_back(1);
    b.push_back(n);
    for(int i = 1;i < m;i++){
    
    
        //printf("%3d%3d%3d\n",a[i].num,a[i].x,a[i].y);
        b.push_back(a[i].x);
        b.push_back(a[i].y);
    }
    sort(b.begin(),b.end());
    ll ans = m;
    for(int i = 0;i < b.size();i++){
    
    
        if(i%2 == 0){
    
    
            ans -= num[b[i]];
        }else {
    
    
            ans += num[b[i]];
        }
    }
    cout<<ans<<endl;
    return 0;
}