平衡的阵容——洛谷——2880——RMQ

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
inline int read(){
    int t=1,num=0;char c=getchar();
    while(c>‘9‘||c<‘0‘){if(c==‘-‘)t=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){num=num*10+c-‘0‘;c=getchar();}
    return num*t;
}
const int maxn=50010;
int n,m,f[maxn][21],ff[maxn][21];
inline int min(int a,int b){return a<b?a:b;}
inline int max(int a,int b){return a>b?a:b;}
int main()
{
    n=read();m=read();
    for(int i=1;i<=n;i++)f[i][0]=ff[i][0]=read();
    for(int j=1;j<21;j++)
      for(int i=1;i<=n;i++)
        if(i+(1<<j)-1<=n)
          f[i][j]=min(f[i][j-1],f[i+(1<<(j-1))][j-1]),
          ff[i][j]=max(ff[i][j-1],ff[i+(1<<(j-1))][j-1]);
    for(int i=1;i<=m;i++){
        int x=read(),y=read();
        int k=(log(y-x+1.0)/log(2.0));
        int a=min(f[x][k],f[y-(1<<k)+1][k]);
        int b=max(ff[x][k],ff[y-(1<<k)+1][k]);
        printf("%d\n",b-a);
    }
    return 0;
}