【BZOJ 2457】 双端队列

【题目链接】

https://www.lydsy.com/JudgeOnline/problem.php?id=2457

【算法】

贪心

【代码】

#include<bits/stdc++.h>
using namespace std;
#define MAXN 200010

int i,n,len,last,cnt;
int d[MAXN],tmp[MAXN],mx[MAXN],nx[MAXN];
bool flag;

inline bool cmp(int a,int b)
{
        return (d[a] == d[b]) ? (a < b) : (d[a] < d[b]);
}

int main()
{

        scanf("%d",&n);
        for (i = ; i <= n; i++)
        {
                scanf("%d",&d[i]);
                tmp[i] = i;
        }
        sort(tmp+,tmp+n+,cmp);
        d[] = -;
        for (i = ; i <= n; i++)
        {
                if (d[tmp[i]] != d[tmp[i-]])
                {
                        len++;
                        nx[len] = mx[len] = tmp[i];
                }    else
                {
                        nx[len] = min(nx[len],tmp[i]);
                        mx[len] = max(mx[len],tmp[i]);
                }
        }
        flag = false;
        cnt = ;
        last = nx[];
        for (i = ; i <= len; i++)
        {
                if (flag && nx[i] < last)
                {
                        flag = false;
                        cnt++;
                        last = nx[i];
                        continue;
                }
                if (!flag && mx[i] > last)
                {
                        flag = true;
                        last = mx[i];
                        continue;
                }
                if (!flag && mx[i] < last)
                {
                        last = nx[i];
                        continue;
                }
                if (flag && nx[i] > last) last = mx[i];
        }
        printf("%d\n",cnt);

        return ;

}