[PKU3264]Balanced Lineup

RMQ問題

用的st

#include<cstdio>
using namespace std;
const int maxn=50010;
int RMQ[maxn];
int mm[maxn];
int best1[20][maxn],best2[20][maxn];
int N,Q;
void initRMQ(int n)
{
     int i,j,a,b;
     for(mm[0]=-1,i=1;i<=n;i++)
     mm[i]=((i&(i-1))==0)?mm[i-1]+1:mm[i-1];
     for(i=1;i<=n;i++) {best1[0][i]=i;best2[0][i]=i;}
     for(i=1;i<=mm[n];i++)
     for(j=1;j<=n+1-(1<<i);j++)
     {
       a=best1[i-1][j];
       b=best1[i-1][j+(1<<(i-1))];
       if(RMQ[a]<RMQ[b]) best1[i][j]=a;
       else best1[i][j]=b;
       a=best2[i-1][j];
       b=best2[i-1][j+(1<<(i-1))];
       if(RMQ[a]>RMQ[b]) best2[i][j]=a;
       else best2[i][j]=b;
     }
     return;
}
int minRMQ(int a,int b)
{
    int t;
    t=mm[b-a+1];b-=(1<<t)-1;
    a=best1[t][a];b=best1[t][b];
    return RMQ[a]<RMQ[b]?a:b;
}
int maxRMQ(int a,int b)
{
    int t;
    t=mm[b-a+1];b-=(1<<t)-1;
    a=best2[t][a];b=best2[t][b];
    return RMQ[a]>RMQ[b]?a:b;
}
int main()
{
		scanf("%d%d",&N,&Q);
		for (int i=1;i<=N;i++)
		scanf("%d",&RMQ[i]);
		initRMQ(N);
		for (int i=1;i<=Q;i++)
		{
			int l,r;
			scanf("%d%d",&l,&r);
			printf("%d\n",RMQ[maxRMQ(l,r)]-RMQ[minRMQ(l,r)]);
		}
		return 0;
}