poj 3250 Bad Hair Day 单调栈入门

Bad Hair Day

题意:给n(n <= 800,000)头牛，每头牛都有一个高度h,每头牛都只能看到右边比它矮的牛的头发，将每头牛看到的牛的头发加起来为多少?

思路:每头要进栈的牛，将栈顶比其矮的牛出栈，因为这些牛都没有机会看到更后面的牛了，所以出栈;这时加上栈中的元素个数即可；

#include<iostream>

#include<cstdio>

#include<cstring>

#include<string.h>

#include<algorithm>

#include<vector>

#include<cmath>

#include<stdlib.h>

#include<time.h>

#include<stack>

#include<set>

#include<map>

#include<queue>

using namespace std;

#define rep0(i,l,r) for(int i = (l);i < (r);i++)

#define rep1(i,l,r) for(int i = (l);i <= (r);i++)

#define rep_0(i,r,l) for(int i = (r);i > (l);i--)

#define rep_1(i,r,l) for(int i = (r);i >= (l);i--)

#define MS0(a) memset(a,0,sizeof(a))

#define MS1(a) memset(a,-1,sizeof(a))

#define MSi(a) memset(a,0x3f,sizeof(a))

#define inf 0x3f3f3f3f

#define lson l, m, rt << 1

#define rson m+1, r, rt << 1|1

typedef pair<int,int> PII;

#define A first

#define B second

#define MK make_pair

typedef __int64 ll;

template<typename T>

void read1(T &m)

{

    T x=,f=;char ch=getchar();

    while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}

    while(ch>=''&&ch<=''){x=x*+ch-'';ch=getchar();}

    m = x*f;

}

template<typename T>

void read2(T &a,T &b){read1(a);read1(b);}

template<typename T>

void read3(T &a,T &b,T &c){read1(a);read1(b);read1(c);}

template<typename T>

void out(T a)

{

    if(a>) out(a/);

    putchar(a%+'');

}

const int MAXN = 8e4+;

int stk[MAXN];

int main()

{

    ll p = ,ans = ,n,h;

    read1(n);

    rep0(i,,n){

        read1(h);

        while(p && h >= stk[p]) p--;

        stk[++p] = h;

        ans += p-;

        //cout<<p<<" .. \n";

    }

    printf("%I64d\n",ans);

    return ;

}