[BZOJ 1660] Bad Hair Day

[题目链接]

https://www.lydsy.com/JudgeOnline/problem.php?id=1660

[算法]

Sprease Table + 二分

时间复杂度 ： O(NlogN)

[代码]

#include<bits/stdc++.h>
using namespace std;
#define MAXN 80010
#define MAXLOG 20
typedef long long ll;

ll a[MAXN];
ll f[MAXN][MAXLOG];

template <typename T> inline void read(T &x)
{
        ll f = ; x = ;
        char c = getchar();
        for (; !isdigit(c); c = getchar())
        {
                if (c == '-') f = -f;
        }
        for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';
        x *= f;
}
inline ll rmq(int x,int y)
{
        int k = (int)(log(y - x + ) / log(2.0));
        return max(f[x][k],f[y - ( << k) + ][k]);
}

int main()
{

        int n;
        read(n);
        for (int i = ; i <= n; i++) read(a[i]);
        reverse(a + ,a + n + );
        for (int i = ; i <= n; i++) f[i][] = a[i];
        for (int i = ; i < MAXLOG; i++)
        {
                for (int j = ; j + ( << i) -  <= n; j++)
                {
                        f[j][i] = max(f[j][i - ],f[j + ( << (i - ))][i - ]);
                }
        }
        ll ans = ;
        for (int i = ; i <= n; i++)
        {
                int l = ,r = i - ,t = -;
                while (l <= r)
                {
                        int mid = (l + r) >> ;
                        if (rmq(mid,i - ) < a[i])
                        {
                                t = mid;
                                r = mid - ;
                        } else l = mid + ;
                }
                if (t != -) ans += (ll)(i - t);
        }
        printf("%lld\n",ans);

        return ;

}