单调栈 BZOJ1345 [Baltic2007]序列问题Sequence

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 int n,top,stack[1000010];
 7 long long ans;
 8 int main(){
 9     scanf("%d",&n);
10     stack[0]=0x3f3f3f3f;
11     int x;
12     while(n--){
13         scanf("%d",&x);
14         while(top&&x>=stack[top]){
15             if(x>=stack[top-1])    ans+=stack[top-1],top--;
16             else ans+=x,top--;
17         }
18         stack[++top]=x;
19     }
20     while(top>1) ans+=stack[--top];
21     printf("%lld",ans);
22     return 0;    
23 }