Codeforces 442C Artem and Array （看题解)

Artem and Array

经过分析我们能发现， 如果对于一个a[ i ] <= a[ i + 1 ] && a[ i ] <= a[ i - 1 ]可以直接删掉。

最后剩下一个先增后减的序列， 除了最大的两个都能加上。

#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ull unsigned long long

using namespace std;

const int N = 5e5 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const double PI = acos(-1);

int n, a[N], que[N], top;
LL ans;
int main() {
    scanf("%d", &n);
    for(int i = 1; i <= n; i++) scanf("%d", &a[i]);
    que[++top] = a[1];
    for(int i = 2; i <= n; i++) {
        while(top > 1 && que[top] <= que[top - 1] && que[top] <= a[i]) {
            ans += min(que[top - 1], a[i]);
            top--;
        }
        que[++top] = a[i];
    }
    sort(que + 1, que + 1 + top);
    for(int i = 1; i <= top - 2; i++) ans += que[i];
    printf("%lld
", ans);
    return 0;
}

/*
*/