[CF442C] Artem and Array (贪心＋单调栈优化)

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <vector>
 5 #include <map>
 6 #include <set>
 7 #include <bitset>
 8 #include <cmath>
 9 #include <numeric>
10 #include <iterator>
11 #include <iostream>
12 #include <cstdlib>
13 #include <functional>
14 #include <queue>
15 #include <stack>
16 #include <string>
17 #include <cctype>
18 using namespace std;
19 #define PB push_back
20 #define MP make_pair
21 #define SZ size()
22 #define ST begin()
23 #define ED end()
24 #define CLR clear()
25 #define ZERO(x) memset((x),0,sizeof(x))
26 typedef long long LL;
27 typedef unsigned long long ULL;
28 typedef pair<int,int> PII;
29 const double EPS = 1e-8;
30 
31 const int MAX_N = 5*1e5+100;
32 int n,top;
33 LL st[MAX_N];
34 
35 int main() {
36     cin >> n;
37     top = -1;
38     LL ans = 0;
39     for(int i=0;i<n;i++){
40         LL x;
41         cin >> x;
42         while( top>=1 && st[top]<st[top-1]&&st[top]<=x ){
43             ans += min(st[top-1],x);
44             top--;
45         }
46         st[++top] = x;
47     }
48     sort(st,st+top+1);
49     for(int i=0;i<top-1;i++) ans += st[i];
50     cout << ans << endl;
51     return 0;
52 }