POJ——T 3250 Bad Hair Day
http://poj.org/problem?id=3250
Time Limit: 2000MS | Memory Limit: 65536K | |
Total Submissions: 19619 | Accepted: 6702 |
Description
Some of Farmer John's N cows (1 ≤ N ≤ 80,000) are having a bad hair day! Since each cow is self-conscious about her messy hairstyle, FJ wants to count the number of other cows that can see the top of other cows' heads.
Each cow i has a specified height hi (1 ≤ hi ≤ 1,000,000,000) and is standing in a line of cows all facing east (to the right in our diagrams). Therefore, cow i can see the tops of the heads of cows in front of her (namely cows i+1, i+2, and so on), for as long as these cows are strictly shorter than cow i.
Consider this example:
=
= =
= - = Cows facing right -->
= = =
= - = = =
= = = = = =
1 2 3 4 5 6
Cow#1 can see the hairstyle of cows #2, 3, 4
Cow#2 can see no cow's hairstyle
Cow#3 can see the hairstyle of cow #4
Cow#4 can see no cow's hairstyle
Cow#5 can see the hairstyle of cow 6
Cow#6 can see no cows at all!
Let ci denote the number of cows whose hairstyle is visible from cow i; please compute the sum of c1 through cN.For this example, the desired is answer 3 + 0 + 1 + 0 + 1 + 0 = 5.
Input
Lines 2..N+1: Line i+1 contains a single integer that is the height of cow i.
Output
Sample Input
6 10 3 7 4 12 2
Sample Output
5
Source
1 #include <algorithm> 2 #include <iostream> 3 #include <cstdio> 4 5 using namespace std; 6 7 #define LL long long 8 const int N(1000005); 9 LL Stack[N],top,ans; 10 11 int main() 12 { 13 LL n; cin>>n; 14 for(LL h,i=1;i<=n;i++) 15 { 16 cin>>h; 17 for(;top&&Stack[top]<=h;) top--; 18 ans+=top; Stack[++top]=h; 19 } 20 cout<<ans; 21 return 0; 22 }