http://poj.org/problem?id=3250
|
Bad Hair Day
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 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 Line 1: The number of cows, N. Output Line 1: A single integer that is the sum of c1 through cN. Sample Input 6 10 3 7 4 12 2 Sample Output 5 Source |
#include<stdio.h>
#define N 80010
int Stack[N];
int main()
{
int top = 0, i, n, p;
__int64 sum = 0;
scanf("%d", &n);
for(i=1; i<=n; i++)
{
scanf("%d", &p);
while(top>0 && Stack[top]<=p)
top--;
sum += top;
Stack[++top] = p;
}
printf("%I64d\n", sum);
return 0;
}