POJ 3250 Bad Hair Day (use of stacks)

http://poj.org/problem?id=3250

Bad Hair Day

Time Limit: 2000MS		Memory Limit: 65536K
Total Submissions: 15985		Accepted: 5404

Description

Some of Farmer John ' s n cows (1≤ n ≤80,000) is has a bad hair day! Since Each cow was self-conscious about she messy hairstyle, FJ wants to count the number of other cows so can see the to P of other cows ' heads.

Each cow i have a specified height hi (1≤ hi ≤1,000,000,000) and is standing in a line of cows All facing east (to the right with our diagrams). Therefore, Cow i can see the tops of the heads of cows in front of her (namely cows i+1, i+2, a nd so on), for as long as these cows is strictly shorter than cow I.

Consider this example:

=
=       =
=-= Cows facing right---
=   =   =
= - = = =
= = = = = =

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 are 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.
Lines 2..n+1:line I+1 contains a single integer which is the height of cow I.

Output

Line 1: A single integer which is the sum of C1 through CN.

Sample Input

610374122

Sample Output

5

Main topic:

n number, row from left to right, ask each number to the right of the number of smaller than he has a few, and then sum


You can think back, see how many numbers he has on his left, and then add them up.

To simulate with a stack, first number is pressed into the stack:

If the stack head element s.top () > A[i],

The stack inside the elements are larger than a[i], then the number of larger than a[i] is the number of elements inside the stack s.size ();

Otherwise, the stack Head element s.top () <= A[i], stating that s.top () does not meet the criteria (not greater than a[i])

Then let the stack first element out of the stack, continue to compare the stack within the element if not greater than a[i], let him out of the stack

Which means that the elements in the stack are larger than the a[i].

#include <stdio.h>#include<string.h>#include<stdlib.h>#include<math.h>#include<stack>#include<algorithm>using namespacestd;Const intN =80010; typedef __int64 LL;intA[n];intMain () {stack<int>S; intN;  while(~SCANF ("%d", &N)) {ll sum=0;  for(inti =0; I < n; i++) scanf ("%d", &A[i]); S.push (a[0]);//The first number in a stack         for(inti =1; I < n; i++)//Traverse        {             while(! S.empty () && s.top () <=A[i]) S.pop ();//out of the stackSum + =s.size (); S.push (A[i]);//into the stack} printf ("%i64d\n", sum); }    return 0;}

POJ 3250 Bad Hair Day (use of stacks)